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Contents
Articles
Bacteria
1
''Escherichia coli''
27
Salmonellosis
40
''Clostridium perfringens''
45
References
Article Sources and Contributors
48
Image Sources, Licenses and Contributors
50
Article Licenses
License
51
Bacteria
1
Bacteria
Bacteria
Fossil range: Archean or earlier - Recent
Scanning electron micrograph of Escherichia coli
bacilli
Scientific classification
Domain:
Bacteria
[1]
Phyla
•
gram positive/no outer membrane
Actinobacteria (high-G+C)
Firmicutes (low-G+C)
Tenericutes (no wall)
•
gram negative/outer membrane present
Aquificae
Bacteroidetes/Chlorobi
Chlamydiae/Verrucomicrobia
Deinococcus-Thermus
Fusobacteria
Gemmatimonadetes
Nitrospirae
Proteobacteria
Spirochaetes
Synergistetes
•
unknown/ungrouped
Acidobacteria
Chloroflexi
Chrysiogenetes
Cyanobacteria
Deferribacteres
Dictyoglomi
Fibrobacteres
Planctomycetes
Thermodesulfobacteria
Thermotogae
The bacteria (
[bækˈtɪəriə] Wikipedia:Media helpFile:en-us-bacteria.ogg; singular: bacterium)[α] are a large
group of unicellular, prokaryote, microorganisms. Typically a few micrometres in length, bacteria have a wide range
of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in
soil, acidic hot springs, radioactive waste,[2] water, and deep in the Earth's crust, as well as in organic matter and the
live bodies of plants and animals. There are typically 40 million bacterial cells in a gram of soil and a million
bacterial cells in a millilitre of fresh water; in all, there are approximately five nonillion (5×1030) bacteria on
Bacteria
2
Earth,[3] forming much of the world's biomass.[3] Bacteria are vital in recycling nutrients, with many steps in nutrient
cycles depending on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction.
However, most bacteria have not been characterized, and only about half of the phyla of bacteria have species that
can be grown in the laboratory.[4] The study of bacteria is known as bacteriology, a branch of microbiology.
There are approximately ten times as many bacterial cells in the human flora of bacteria as there are human cells in
the body, with large numbers of bacteria on the skin and as gut flora.[5] The vast majority of the bacteria in the body
are rendered harmless by the protective effects of the immune system, and a few are beneficial. However, a few
species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy and
bubonic plague. The most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing
about 2 million people a year, mostly in sub-Saharan Africa.[6] In developed countries, antibiotics are used to treat
bacterial infections and in agriculture, so antibiotic resistance is becoming common. In industry, bacteria are
important in sewage treatment, the production of cheese and yoghurt through fermentation, as well as in
biotechnology, and the manufacture of antibiotics and other chemicals.[7]
Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells
of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound
organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed
after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved
independently from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.[8]
History of bacteriology
Bacteria were first observed by Antonie van
Leeuwenhoek in 1676, using a single-lens microscope of
his own design.[9] He called them "animalcules" and
published his observations in a series of letters to the
Royal Society.[10] [11] [12] The name bacterium was
introduced much later, by Christian Gottfried Ehrenberg
in 1838.[13]
Louis Pasteur demonstrated in 1859 that the fermentation
process is caused by the growth of microorganisms, and
that this growth is not due to spontaneous generation.
(Yeasts and molds, commonly associated with
fermentation, are not bacteria, but rather fungi.) Along
with his contemporary, Robert Koch, Pasteur was an
early advocate of the germ theory of disease.[14] Robert
Koch was a pioneer in medical microbiology and worked
on cholera, anthrax and tuberculosis. In his research into
tuberculosis, Koch finally proved the germ theory, for
which he was awarded a Nobel Prize in 1905.[15] In
Koch's postulates, he set out criteria to test if an organism
is the cause of a disease; these postulates are still used
today.[16]
Antonie van Leeuwenhoek, the first microbiologist and the first
person to observe bacteria using a microscope.
Though it was known in the nineteenth century that bacteria are the cause of many diseases, no effective antibacterial
treatments were available.[17] In 1910, Paul Ehrlich developed the first antibiotic, by changing dyes that selectively
stained Treponema pallidum—the spirochaete that causes syphilis—into compounds that selectively killed the
pathogen.[18] Ehrlich had been awarded a 1908 Nobel Prize for his work on immunology, and pioneered the use of
Bacteria
3
stains to detect and identify bacteria, with his work being the basis of the Gram stain and the Ziehl-Neelsen stain.[19]
A major step forward in the study of bacteria was the recognition in 1977 by Carl Woese that archaea have a separate
line of evolutionary descent from bacteria.[20] This new phylogenetic taxonomy was based on the sequencing of 16S
ribosomal RNA, and divided prokaryotes into two evolutionary domains, as part of the three-domain system.[21]
Origin and early evolution
The ancestors of modern bacteria were single-celled microorganisms that were the first forms of life to develop on
earth, about 4 billion years ago. For about 3 billion years, all organisms were microscopic, and bacteria and archaea
were the dominant forms of life.[22] [23] Although bacterial fossils exist, such as stromatolites, their lack of
distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the
time of origin of a particular bacterial species. However, gene sequences can be used to reconstruct the bacterial
phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage.[24] The most
recent common ancestor of bacteria and archaea was probably a hyperthermophile that lived about 2.5 billion–3.2
billion years ago.[25] [26]
Bacteria were also involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here,
eukaryotes resulted from ancient bacteria entering into endosymbiotic associations with the ancestors of eukaryotic
cells, which were themselves possibly related to the Archaea.[27] [28] This involved the engulfment by
proto-eukaryotic cells of alpha-proteobacterial symbionts to form either mitochondria or hydrogenosomes, which are
still found in all known Eukarya (sometimes in highly reduced form, e.g. in ancient "amitochondrial" protozoa).
Later on, some eukaryotes that already contained mitochondria also engulfed cyanobacterial-like organisms. This led
to the formation of chloroplasts in algae and plants. There are also some algae that originated from even later
endosymbiotic events. Here, eukaryotes engulfed a eukaryotic algae that developed into a "second-generation"
plastid.[29] [30] This is known as secondary endosymbiosis.
Morphology
Bacteria display a wide diversity of
shapes and sizes, called morphologies.
Bacterial cells are about one tenth the
size of eukaryotic cells and are
typically
0.5–5.0 micrometres
in
length. However, a few species–for
example Thiomargarita namibiensis
and Epulopiscium fishelsoni–are up to
half a millimetre long and are visible to
the unaided eye.[31] Among the
smallest bacteria are members of the
genus Mycoplasma, which measure
only 0.3 micrometres, as small as the
largest viruses.[32] Some bacteria may
be
even
smaller,
but
these
ultramicrobacteria
are
not
[33]
well-studied.
Bacteria display many cell morphologies and arrangements
Bacteria
Most bacterial species are either spherical, called cocci (sing. coccus, from Greek kókkos, grain, seed) or rod-shaped,
called bacilli (sing. bacillus, from Latin baculus, stick). Elongation is associated with swimming.[34] Some
rod-shaped bacteria, called vibrio, are slightly curved or comma-shaped; others, can be spiral-shaped, called spirilla,
or tightly coiled, called spirochaetes. A small number of species even have tetrahedral or cuboidal shapes.[35] More
recently, bacteria were discovered deep under the Earth's crust that grow as long rods with a star-shaped
cross-section. The large surface area to volume ratio of this morphology may give these bacteria an advantage in
nutrient-poor environments.[36] This wide variety of shapes is determined by the bacterial cell wall and cytoskeleton,
and is important because it can influence the ability of bacteria to acquire nutrients, attach to surfaces, swim through
liquids and escape predators.[37] [38]
Many bacterial species exist simply as single cells, others associate in characteristic patterns: Neisseria form diploids
(pairs), Streptococcus form chains, and Staphylococcus group together in "bunch of grapes" clusters. Bacteria can
also be elongated to form filaments, for example the Actinobacteria. Filamentous bacteria are often surrounded by a
sheath that contains many individual cells. Certain types, such as species of the genus Nocardia, even form complex,
branched filaments, similar in appearance to fungal mycelia.[39]
Bacteria often attach to surfaces and form
dense aggregations called biofilms or
bacterial mats. These films can range
from a few micrometers in thickness to up
to half a meter in depth, and may contain
multiple species of bacteria, protists and
archaea. Bacteria living in biofilms
display a complex arrangement of cells
and extracellular components, forming
secondary
structures
such
as
microcolonies, through which there are
networks of channels to enable better
diffusion of nutrients.[40] [41] In natural
environments, such as soil or the surfaces
of plants, the majority of bacteria are
bound to surfaces in biofilms.[42] Biofilms
The range of sizes shown by prokaryotes, relative to those of other organisms and
are also important in medicine, as these
biomolecules
structures are often present during chronic
bacterial infections or in infections of
implanted medical devices, and bacteria protected within biofilms are much harder to kill than individual isolated
bacteria.[43]
Even more complex morphological changes are sometimes possible. For example, when starved of amino acids,
Myxobacteria detect surrounding cells in a process known as quorum sensing, migrate towards each other, and
aggregate to form fruiting bodies up to 500 micrometres long and containing approximately 100,000 bacterial
cells.[44] In these fruiting bodies, the bacteria perform separate tasks; this type of cooperation is a simple type of
multicellular organisation. For example, about one in 10 cells migrate to the top of these fruiting bodies and
differentiate into a specialised dormant state called myxospores, which are more resistant to drying and other adverse
environmental conditions than are ordinary cells.[45]
4
Bacteria
5
Cellular structure
Intracellular structures
The bacterial cell is surrounded by a lipid
membrane, or cell membrane, which encloses
the contents of the cell and acts as a barrier to
hold nutrients, proteins and other essential
components of the cytoplasm within the cell. As
they are prokaryotes, bacteria do not tend to
have membrane-bound organelles in their
cytoplasm and thus contain few large
intracellular structures. They consequently lack a
nucleus, mitochondria, chloroplasts and the other
organelles present in eukaryotic cells, such as the
Golgi apparatus and endoplasmic reticulum.[46]
Bacteria were once seen as simple bags of
Structure and contents of a typical Gram positive bacterial cell
cytoplasm, but elements such as prokaryotic
cytoskeleton,[47] [48] and the localization of
proteins to specific locations within the cytoplasm[49] have been found to show levels of complexity. These
subcellular compartments have been called "bacterial hyperstructures".[50]
Micro-compartments such as carboxysome[51] provides a further level of organization, which are compartments
within bacteria that are surrounded by polyhedral protein shells, rather than by lipid membranes.[52] These
"polyhedral organelles" localize and compartmentalize bacterial metabolism, a function performed by the
membrane-bound organelles in eukaryotes.[53] [54]
Many important biochemical reactions, such as energy generation, occur by concentration gradients across
membranes, a potential difference also found in a battery. The general lack of internal membranes in bacteria means
reactions such as electron transport occur across the cell membrane between the cytoplasm and the periplasmic
space.[55] However, in many photosynthetic bacteria the plasma membrane is highly folded and fills most of the cell
with layers of light-gathering membrane.[56] These light-gathering complexs may even form lipid-enclosed structures
called chlorosomes in green sulfur bacteria.[57] Other proteins import nutrients across the cell membrane, or to expel
undesired molecules from the cytoplasm.
Carboxysomes are protein-enclosed bacterial organelles. Top left is an electron
microscope image of carboxysomes in Halothiobacillus neapolitanus, below is an image
of purified carboxysomes. On the right is a model of their structure. Scale bars are
[58]
100 nm.
Bacteria
do
not
have
a
membrane-bound nucleus, and their
genetic material is typically a single
circular chromosome located in the
cytoplasm in an irregularly shaped
body called the nucleoid.[59] The
nucleoid contains the chromosome
with associated proteins and RNA. The
order Planctomycetes are an exception
to the general absence of internal
membranes in bacteria, because they
have a membrane around their
Bacteria
6
nucleoid and contain other membrane-bound cellular structures.[60] Like all living organisms, bacteria contain
ribosomes for the production of proteins, but the structure of the bacterial ribosome is different from those of
eukaryotes and Archaea.[61]
Some bacteria produce intracellular nutrient storage granules, such as glycogen,[62] polyphosphate,[63] sulfur[64] or
polyhydroxyalkanoates.[65] These granules enable bacteria to store compounds for later use. Certain bacterial
species, such as the photosynthetic Cyanobacteria, produce internal gas vesicles, which they use to regulate their
buoyancy - allowing them to move up or down into water layers with different light intensities and nutrient levels.[66]
Extracellular structures
Around the outside of the cell membrane is the bacterial cell wall. Bacterial cell walls are made of peptidoglycan
(called murein in older sources), which is made from polysaccharide chains cross-linked by unusual peptides
containing D-amino acids.[67] Bacterial cell walls are different from the cell walls of plants and fungi, which are
made of cellulose and chitin, respectively.[68] The cell wall of bacteria is also distinct from that of Archaea, which do
not contain peptidoglycan. The cell wall is essential to the survival of many bacteria, and the antibiotic penicillin is
able to kill bacteria by inhibiting a step in the synthesis of peptidoglycan.[68]
There are broadly speaking two different types of cell wall in bacteria, called Gram-positive and Gram-negative. The
names originate from the reaction of cells to the Gram stain, a test long-employed for the classification of bacterial
species.[69]
Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids. In
contrast, Gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan
surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins. Most bacteria have the
Gram-negative cell wall, and only the Firmicutes and Actinobacteria (previously known as the low G+C and high
G+C Gram-positive bacteria, respectively) have the alternative Gram-positive arrangement.[70] These differences in
structure can produce differences in antibiotic susceptibility; for instance, vancomycin can kill only Gram-positive
bacteria and is ineffective against Gram-negative pathogens, such as Haemophilus influenzae or Pseudomonas
aeruginosa.[71]
In many bacteria an S-layer of rigidly arrayed protein molecules covers the outside of the cell.[72] This layer provides
chemical and physical protection for the cell surface and can act as a macromolecular diffusion barrier. S-layers have
diverse but mostly poorly understood functions, but are known to act as virulence factors in Campylobacter and
contain surface enzymes in Bacillus stearothermophilus.[73]
Flagella are rigid protein structures, about
20 nanometres in diameter and up to 20 micrometres in
length, that are used for motility. Flagella are driven by
the energy released by the transfer of ions down an
electrochemical gradient across the cell membrane.[74]
Fimbriae are fine filaments of protein, just
2–10 nanometres in diameter and up to several
micrometers in length. They are distributed over the
surface of the cell, and resemble fine hairs when seen
under the electron microscope. Fimbriae are believed to
be involved in attachment to solid surfaces or to other
Helicobacter pylori electron micrograph, showing multiple flagella
on the cell surface
cells and are essential for the virulence of some
bacterial pathogens.[75] Pili (sing. pilus) are cellular
appendages, slightly larger than fimbriae, that can transfer genetic material between bacterial cells in a process called
conjugation (see bacterial genetics, below).[76]
Bacteria
Capsules or slime layers are produced by many bacteria to surround their cells, and vary in structural complexity:
ranging from a disorganised slime layer of extra-cellular polymer, to a highly structured capsule or glycocalyx.
These structures can protect cells from engulfment by eukaryotic cells, such as macrophages.[77] They can also act as
antigens and be involved in cell recognition, as well as aiding attachment to surfaces and the formation of
biofilms.[78]
The assembly of these extracellular structures is dependent on bacterial secretion systems. These transfer proteins
from the cytoplasm into the periplasm or into the environment around the cell. Many types of secretion systems are
known and these structures are often essential for the virulence of pathogens, so are intensively studied.[79]
Endospores
Certain genera of Gram-positive bacteria, such as
Bacillus, Clostridium, Sporohalobacter, Anaerobacter
and Heliobacterium, can form highly resistant, dormant
structures called endospores.[80] In almost all cases, one
endospore is formed and this is not a reproductive
process, although Anaerobacter can make up to seven
endospores in a single cell.[81] Endospores have a
central core of cytoplasm containing DNA and
ribosomes surrounded by a cortex layer and protected
by an impermeable and rigid coat.
Endospores show no detectable metabolism and can
Bacillus anthracis (stained purple) growing in cerebrospinal fluid
survive extreme physical and chemical stresses, such as
high levels of UV light, gamma radiation, detergents, disinfectants, heat, pressure and desiccation.[82] In this dormant
state, these organisms may remain viable for millions of years,[83] [84] and endospores even allow bacteria to survive
exposure to the vacuum and radiation in space.[85] Endospore-forming bacteria can also cause disease: for example,
anthrax can be contracted by the inhalation of Bacillus anthracis endospores, and contamination of deep puncture
wounds with Clostridium tetani endospores causes tetanus.[86]
Metabolism
Bacteria exhibit an extremely wide variety of metabolic types.[87] The distribution of metabolic traits within a group
of bacteria has traditionally been used to define their taxonomy, but these traits often do not correspond with modern
genetic classifications.[88] Bacterial metabolism is classified into nutritional groups on the basis of three major
criteria: the kind of energy used for growth, the source of carbon, and the electron donors used for growth. An
additional criterion of respiratory microorganisms are the electron acceptors used for aerobic or anaerobic
respiration.[89]
7
Bacteria
8
Nutritional types in bacterial metabolism
Nutritional
type
Source of
energy
Source of carbon
Examples
Phototrophs
Sunlight
Organic compounds (photoheterotrophs) or carbon
fixation (photoautotrophs)
Cyanobacteria, Green sulfur bacteria, Chloroflexi,
or Purple bacteria
Lithotrophs
Inorganic
compounds
Organic compounds (lithoheterotrophs) or carbon
fixation (lithoautotrophs)
Thermodesulfobacteria, Hydrogenophilaceae, or
Nitrospirae
Organotrophs
Organic
compounds
Organic compounds (chemoheterotrophs) or carbon
fixation (chemoautotrophs)
Bacillus, Clostridium or Enterobacteriaceae
Carbon metabolism in bacteria is either heterotrophic, where organic carbon compounds are used as carbon sources,
or autotrophic, meaning that cellular carbon is obtained by fixing carbon dioxide. Heterotrophic bacteria include
parasitic types. Typical autotrophic bacteria are phototrophic cyanobacteria, green sulfur-bacteria and some purple
bacteria, but also many chemolithotrophic species, such as nitrifying or sulfur-oxidising bacteria.[90] Energy
metabolism of bacteria is either based on phototrophy, the use of light through photosynthesis, or on chemotrophy,
the use of chemical substances for energy, which are mostly oxidised at the expense of oxygen or alternative electron
acceptors (aerobic/anaerobic respiration).
Finally, bacteria are further divided into lithotrophs that use
inorganic electron donors and organotrophs that use organic
compounds as electron donors. Chemotrophic organisms use the
respective electron donors for energy conservation (by
aerobic/anaerobic respiration or fermentation) and biosynthetic
reactions (e.g. carbon dioxide fixation), whereas phototrophic
organisms use them only for biosynthetic purposes. Respiratory
organisms use chemical compounds as a source of energy by
taking electrons from the reduced substrate and transferring them
to a terminal electron acceptor in a redox reaction. This reaction
releases energy that can be used to synthesise ATP and drive
Filaments of photosynthetic cyanobacteria
metabolism. In aerobic organisms, oxygen is used as the electron
acceptor. In anaerobic organisms other inorganic compounds, such
as nitrate, sulfate or carbon dioxide are used as electron acceptors. This leads to the ecologically important processes
of denitrification, sulfate reduction and acetogenesis, respectively.
Another way of life of chemotrophs in the absence of possible electron acceptors is fermentation, where the electrons
taken from the reduced substrates are transferred to oxidised intermediates to generate reduced fermentation products
(e.g. lactate, ethanol, hydrogen, butyric acid). Fermentation is possible, because the energy content of the substrates
is higher than that of the products, which allows the organisms to synthesise ATP and drive their metabolism.[91] [92]
These processes are also important in biological responses to pollution; for example, sulfate-reducing bacteria are
largely responsible for the production of the highly toxic forms of mercury (methyl- and dimethylmercury) in the
environment.[93] Non-respiratory anaerobes use fermentation to generate energy and reducing power, secreting
metabolic by-products (such as ethanol in brewing) as waste. Facultative anaerobes can switch between fermentation
and different terminal electron acceptors depending on the environmental conditions in which they find themselves.
Lithotrophic bacteria can use inorganic compounds as a source of energy. Common inorganic electron donors are
hydrogen, carbon monoxide, ammonia (leading to nitrification), ferrous iron and other reduced metal ions, and
several reduced sulfur compounds. Unusually, the gas methane can be used by methanotrophic bacteria as both a
source of electrons and a substrate for carbon anabolism.[94] In both aerobic phototrophy and chemolithotrophy,
oxygen is used as a terminal electron acceptor, while under anaerobic conditions inorganic compounds are used
Bacteria
9
instead. Most lithotrophic organisms are autotrophic, whereas organotrophic organisms are heterotrophic.
In addition to fixing carbon dioxide in photosynthesis, some bacteria also fix nitrogen gas (nitrogen fixation) using
the enzyme nitrogenase. This environmentally important trait can be found in bacteria of nearly all the metabolic
types listed above, but is not universal.[95]
Growth and reproduction
Unlike multicellular organisms, increases in the size of bacteria (cell
growth) and their reproduction by cell division are tightly linked in
unicellular organisms. Bacteria grow to a fixed size and then reproduce
through binary fission, a form of asexual reproduction.[96] Under
optimal conditions, bacteria can grow and divide extremely rapidly, and
bacterial populations can double as quickly as every 9.8 minutes.[97] In
cell division, two identical clone daughter cells are produced. Some
bacteria, while still reproducing asexually, form more complex
reproductive structures that help disperse the newly formed daughter
cells. Examples include fruiting body formation by Myxobacteria and
aerial hyphae formation by Streptomyces, or budding. Budding involves
a cell forming a protrusion that breaks away and produces a daughter
cell.
Many bacteria reproduce through binary fission
In the laboratory, bacteria are usually grown
using solid or liquid media. Solid growth
media such as agar plates are used to isolate
pure cultures of a bacterial strain. However,
liquid growth media are used when
measurement of growth or large volumes of
cells are required. Growth in stirred liquid
media occurs as an even cell suspension,
making the cultures easy to divide and
transfer, although isolating single bacteria
from liquid media is difficult. The use of
selective media (media with specific
nutrients added or deficient, or with
antibiotics added) can help identify specific
organisms.[99]
Most laboratory techniques for growing
bacteria use high levels of nutrients to
[98]
A growing colony of Escherichia coli cells
produce large amounts of cells cheaply and
quickly. However, in natural environments
nutrients are limited, meaning that bacteria cannot continue to reproduce indefinitely. This nutrient limitation has led
the evolution of different growth strategies (see r/K selection theory). Some organisms can grow extremely rapidly
when nutrients become available, such as the formation of algal (and cyanobacterial) blooms that often occur in
lakes during the summer.[100] Other organisms have adaptations to harsh environments, such as the production of
multiple antibiotics by Streptomyces that inhibit the growth of competing microorganisms.[101] In nature, many
organisms live in communities (e.g. biofilms) which may allow for increased supply of nutrients and protection from
environmental stresses.[42] These relationships can be essential for growth of a particular organism or group of
Bacteria
organisms (syntrophy).[102]
Bacterial growth follows three phases. When a population of bacteria first enter a high-nutrient environment that
allows growth, the cells need to adapt to their new environment. The first phase of growth is the lag phase, a period
of slow growth when the cells are adapting to the high-nutrient environment and preparing for fast growth. The lag
phase has high biosynthesis rates, as proteins necessary for rapid growth are produced.[103] The second phase of
growth is the logarithmic phase (log phase), also known as the exponential phase. The log phase is marked by rapid
exponential growth. The rate at which cells grow during this phase is known as the growth rate (k), and the time it
takes the cells to double is known as the generation time (g). During log phase, nutrients are metabolised at
maximum speed until one of the nutrients is depleted and starts limiting growth. The final phase of growth is the
stationary phase and is caused by depleted nutrients. The cells reduce their metabolic activity and consume
non-essential cellular proteins. The stationary phase is a transition from rapid growth to a stress response state and
there is increased expression of genes involved in DNA repair, antioxidant metabolism and nutrient transport.[104]
Genetics
Most bacteria have a single circular chromosome that can range in size from only 160,000 base pairs in the
endosymbiotic bacteria Candidatus Carsonella ruddii,[105] to 12,200,000 base pairs in the soil-dwelling bacteria
Sorangium cellulosum.[106] Spirochaetes of the genus Borrelia are a notable exception to this arrangement, with
bacteria such as Borrelia burgdorferi, the cause of Lyme disease, containing a single linear chromosome.[107] The
genes in bacterial genomes are usually a single continuous stretch of DNA and although several different types of
introns do exist in bacteria, these are much more rare than in eukaryotes.[108]
Bacteria may also contain plasmids, which are small extra-chromosomal DNAs that may contain genes for antibiotic
resistance or virulence factors.
Bacteria, as asexual organisms, inherit identical copies of their parent's genes (i.e., they are clonal). However, all
bacteria can evolve by selection on changes to their genetic material DNA caused by genetic recombination or
mutations. Mutations come from errors made during the replication of DNA or from exposure to mutagens. Mutation
rates vary widely among different species of bacteria and even among different clones of a single species of
bacteria.[109] Genetic changes in bacterial genomes come from either random mutation during replication or
"stress-directed mutation", where genes involved in a particular growth-limiting process have an increased mutation
rate.[110]
Some bacteria also transfer genetic material between cells. This can occur in three main ways. Firstly, bacteria can
take up exogenous DNA from their environment, in a process called transformation. Genes can also be transferred by
the process of transduction, when the integration of a bacteriophage introduces foreign DNA into the chromosome.
The third method of gene transfer is bacterial conjugation, where DNA is transferred through direct cell contact. This
gene acquisition from other bacteria or the environment is called horizontal gene transfer and may be common under
natural conditions.[111] Gene transfer is particularly important in antibiotic resistance as it allows the rapid transfer of
resistance genes between different pathogens.[112]
Bacteriophages
Bacteriophages are viruses that change the bacterial DNA. Many types of bacteriophage exist, some simply infect
and lyse their host bacteria, while others insert into the bacterial chromosome. A bacteriophage can contain genes
that contribute to its host's phenotype: for example, in the evolution of Escherichia coli O157:H7 and Clostridium
botulinum, the toxin genes in an integrated phage converted a harmless ancestral bacteria into a lethal pathogen.[113]
Bacteria resist phage infection through restriction modification systems that degrade foreign DNA,[114] and a system
that uses CRISPR sequences to retain fragments of the genomes of phage that the bacteria have come into contact
with in the past, which allows them to block virus replication through a form of RNA interference.[115] [116] This
CRISPR system provides bacteria with acquired immunity to infection.
10
Bacteria
Behavior
Secretion
Bacteria frequently secrete chemicals into their environment in order to modify it favorably. The secretions are often
proteins and may act as enzymes that digest some form of food in the environment.
Bioluminescence
A few bacteria have chemical systems that generate light. This bioluminescence often occurs in bacteria that live in
association with fish, and the light probably serves to attract fish or other large animals.[117]
Multicellularity
(See also: Prokaryote#Sociality)
Bacteria often function as multicellular aggregates known as biofilms, exchanging a variety of molecular signals for
inter-cell communication, and engaging in coordinated multicellular behavior.[118] [119]
The communal benefits of multicellular cooperation include a cellular division of labor, accessing resources that
cannot effectively be utilized by single cells, collectively defending against antagonists, and optimizing population
survival by differentiating into distinct cell types.[118] For example, bacteria in biofilms can have more than 500
times increased resistance to antibacterial agents than individual "planktonic" bacteria of the same species.[119]
One type of inter-cellular communication by a molecular signal is called quorum sensing, which serves the purpose
of determining whether there is a local population density that is sufficiently high that it is productive to invest in
processes that are only successful if large numbers of similar organisms behave similarly, as in excreting digestive
enzymes or emitting light.
It is thought that bacteria are too small to use pheromones to attract other individuals, as is common among
animals.[120]
11
Bacteria
12
Movement
Many bacteria can move using a variety of mechanisms: flagella are used for swimming through water; bacterial
gliding and twitching motility move bacteria across surfaces; and changes of buoyancy allow vertical motion.[121]
Swimming bacteria frequently move
near 10 body lengths per second and a
few as fast as 100. This makes them at
least as fast as fish, on a relative
scale.[122]
In twitching motility, bacterial use
their type IV pili as a grappling hook,
repeatedly extending it, anchoring it
and then retracting it with remarkable
force (>80 pN).[123]
Flagella are semi-rigid cylindrical
structures that are rotated and function
much like the propeller on a ship.
Objects as small as bacteria operate a
low Reynolds number and cylindrical
forms are more efficient that the flat,
paddle-like, forms appropriate at
human size scale.[124]
Flagellum of Gram-negative Bacteria. The base drives the rotation of the hook and
filament.
Bacterial species differ in the number
and arrangement of flagella on their
surface; some have a single flagellum (monotrichous), a flagellum at each end (amphitrichous), clusters of flagella at
the poles of the cell (lophotrichous), while others have flagella distributed over the entire surface of the cell
(peritrichous). The bacterial flagella is the best-understood motility structure in any organism and is made of about
20 proteins, with approximately another 30 proteins required for its regulation and assembly.[121] The flagellum is a
rotating structure driven by a reversible motor at the base that uses the electrochemical gradient across the membrane
for power.[125] This motor drives the motion of the filament, which acts as a propeller.
Many bacteria (such as E. coli) have two distinct modes of movement: forward movement (swimming) and
tumbling. The tumbling allows them to reorient and makes their movement a three-dimensional random walk.[126]
(See external links below for link to videos.) The flagella of a unique group of bacteria, the spirochaetes, are found
between two membranes in the periplasmic space. They have a distinctive helical body that twists about as it
moves.[121]
Motile bacteria are attracted or repelled by certain stimuli in behaviors called taxes: these include chemotaxis,
phototaxis and magnetotaxis.[127] [128] In one peculiar group, the myxobacteria, individual bacteria move together to
form waves of cells that then differentiate to form fruiting bodies containing spores.[45] The myxobacteria move only
when on solid surfaces, unlike E. coli which is motile in liquid or solid media.
Several Listeria and Shigella species move inside host cells by usurping the cytoskeleton, which is normally used to
move organelles inside the cell. By promoting actin polymerization at one pole of their cells, they can form a kind of
tail that pushes them through the host cell's cytoplasm.[129]
Bacteria
Classification and identification
Classification seeks to describe the diversity of bacterial species
by naming and grouping organisms based on similarities. Bacteria
can be classified on the basis of cell structure, cellular metabolism
or on differences in cell components such as DNA, fatty acids,
pigments, antigens and quinones.[99] While these schemes allowed
the identification and classification of bacterial strains, it was
unclear whether these differences represented variation between
distinct species or between strains of the same species. This
uncertainty was due to the lack of distinctive structures in most
bacteria, as well as lateral gene transfer between unrelated
Streptococcus mutans visualized with a Gram stain
species.[130] Due to lateral gene transfer, some closely related
bacteria can have very different morphologies and metabolisms.
To overcome this uncertainty, modern bacterial classification emphasizes molecular systematics, using genetic
techniques such as guanine cytosine ratio determination, genome-genome hybridization, as well as sequencing genes
that have not undergone extensive lateral gene transfer, such as the rRNA gene.[131] Classification of bacteria is
determined by publication in the International Journal of Systematic Bacteriology,[132] and Bergey's Manual of
Systematic Bacteriology.[133] The International Committee on Systematic Bacteriology (ICSB) maintains
international rules for the naming of bacteria and taxonomic categories and for the ranking of them in the
International Code of Nomenclature of Bacteria.
The term "bacteria" was traditionally applied to all microscopic, single-celled prokaryotes. However, molecular
systematics showed prokaryotic life to consist of two separate domains, originally called Eubacteria and
Archaebacteria, but now called Bacteria and Archaea that evolved independently from an ancient common
ancestor.[8] The archaea and eukaryotes are more closely related to each other than either is to the bacteria. These
two domains, along with Eukarya, are the basis of the three-domain system, which is currently the most widely used
classification system in microbiolology.[134] However, due to the relatively recent introduction of molecular
systematics and a rapid increase in the number of genome sequences that are available, bacterial classification
remains a changing and expanding field.[4] [135] For example, a few biologists argue that the Archaea and Eukaryotes
evolved from Gram-positive bacteria.[136]
Identification of bacteria in the laboratory is particularly relevant in medicine, where the correct treatment is
determined by the bacterial species causing an infection. Consequently, the need to identify human pathogens was a
major impetus for the development of techniques to identify bacteria.
13
Bacteria
The Gram stain, developed in 1884 by
Hans Christian Gram, characterises
bacteria based on the structural
characteristics of their cell walls.[69]
The thick layers of peptidoglycan in
the "Gram-positive" cell wall stain
purple, while the thin "Gram-negative"
cell wall appears pink. By combining
morphology and Gram-staining, most
bacteria can be classified as belonging
to one of four groups (Gram-positive
cocci,
Gram-positive
bacilli,
Gram-negative
cocci
and
Gram-negative
bacilli).
Some
Phylogenetic tree showing the diversity of bacteria, compared to other
organisms
are
best
identified
by
stains
organisms.Ciccarelli FD, Doerks T, von Mering C, Creevey CJ, Snel B, Bork P (2006).
"Toward automatic reconstruction of a highly resolved tree of life". Science 311 (5765):
other than the Gram stain, particularly
1283–7. doi:10.1126/science.1123061. PMID 16513982. Eukaryotes are colored red,
mycobacteria or Nocardia, which show
archaea green and bacteria blue.
acid-fastness on Ziehl–Neelsen or
similar stains.[137] Other organisms
may need to be identified by their growth in special media, or by other techniques, such as serology.
Culture techniques are designed to promote the growth and identify particular bacteria, while restricting the growth
of the other bacteria in the sample. Often these techniques are designed for specific specimens; for example, a
sputum sample will be treated to identify organisms that cause pneumonia, while stool specimens are cultured on
selective media to identify organisms that cause diarrhoea, while preventing growth of non-pathogenic bacteria.
Specimens that are normally sterile, such as blood, urine or spinal fluid, are cultured under conditions designed to
grow all possible organisms.[99] [138] Once a pathogenic organism has been isolated, it can be further characterised
by its morphology, growth patterns such as (aerobic or anaerobic growth, patterns of hemolysis) and staining.
As with bacterial classification, identification of bacteria is increasingly using molecular methods. Diagnostics using
such DNA-based tools, such as polymerase chain reaction, are increasingly popular due to their specificity and
speed, compared to culture-based methods.[139] These methods also allow the detection and identification of "viable
but nonculturable" cells that are metabolically active but non-dividing.[140] However, even using these improved
methods, the total number of bacterial species is not known and cannot even be estimated with any certainty.
Following present classification, there are fewer than 9,000 known species of bacteria (including cyanobacteria)[141]
, but attempts to estimate the true level of bacterial diversity have ranged from 107 to 109 total species - and even
these diverse estimates may be off by many orders of magnitude.[142] [143]
14
Bacteria
Interactions with other organisms
Despite their apparent simplicity, bacteria can form complex associations with other organisms. These symbiotic
associations can be divided into parasitism, mutualism and commensalism. Due to their small size, commensal
bacteria are ubiquitous and grow on animals and plants exactly as they will grow on any other surface. However,
their growth can be increased by warmth and sweat, and large populations of these organisms in humans are the
cause of body odor.
Predators
Some species of bacteria kill and then consume other microorganisms, these species called predatory bacteria.[144]
These include organisms such as Myxococcus xanthus, which forms swarms of cells that kill and digest any bacteria
they encounter.[145] Other bacterial predators either attach to their prey in order to digest them and absorb nutrients,
such as Vampirococcus, or invade another cell and multiply inside the cytosol, such as Daptobacter.[146] These
predatory bacteria are thought to have evolved from saprophages that consumed dead microorganisms, through
adaptations that allowed them to entrap and kill other organisms.[147]
Mutualists
Certain bacteria form close spatial associations that are essential for their survival. One such mutualistic association,
called interspecies hydrogen transfer, occurs between clusters of anaerobic bacteria that consume organic acids such
as butyric acid or propionic acid and produce hydrogen, and methanogenic Archaea that consume hydrogen.[148] The
bacteria in this association are unable to consume the organic acids as this reaction produces hydrogen that
accumulates in their surroundings. Only the intimate association with the hydrogen-consuming Archaea keeps the
hydrogen concentration low enough to allow the bacteria to grow.
In soil, microorganisms which reside in the rhizosphere (a zone that includes the root surface and the soil that
adheres to the root after gentle shaking) carry out nitrogen fixation, converting nitrogen gas to nitrogenous
compounds.[149] This serves to provide an easily absorbable form of nitrogen for many plants, which cannot fix
nitrogen themselves. Many other bacteria are found as symbionts in humans and other organisms. For example, the
presence of over 1,000 bacterial species in the normal human gut flora of the intestines can contribute to gut
immunity, synthesise vitamins such as folic acid, vitamin K and biotin, convert milk protein to lactic acid (see
Lactobacillus), as well as fermenting complex undigestible carbohydrates.[150] [151] [152] The presence of this gut
flora also inhibits the growth of potentially pathogenic bacteria (usually through competitive exclusion) and these
beneficial bacteria are consequently sold as probiotic dietary supplements.[153]
15
Bacteria
16
Pathogens
If bacteria form a parasitic association with other
organisms, they are classed as pathogens. Pathogenic
bacteria are a major cause of human death and disease
and cause infections such as tetanus, typhoid fever,
diphtheria, syphilis, cholera, foodborne illness, leprosy
and tuberculosis. A pathogenic cause for a known
medical disease may only be discovered many years
after, as was the case with Helicobacter pylori and
peptic ulcer disease. Bacterial diseases are also
important in agriculture, with bacteria causing leaf
spot, fire blight and wilts in plants, as well as Johne's
disease, mastitis, salmonella and anthrax in farm
animals.
Color-enhanced scanning electron micrograph showing Salmonella
typhimurium (red) invading cultured human cells
Each species of pathogen has a characteristic spectrum
of interactions with its human hosts. Some organisms, such as Staphylococcus or Streptococcus, can cause skin
infections, pneumonia, meningitis and even overwhelming sepsis, a systemic inflammatory response producing
shock, massive vasodilation and death.[154] Yet these organisms are also part of the normal human flora and usually
exist on the skin or in the nose without causing any disease at all. Other organisms invariably cause disease in
humans, such as the Rickettsia, which are obligate intracellular parasites able to grow and reproduce only within the
cells of other organisms. One species of Rickettsia causes typhus, while another causes Rocky Mountain spotted
fever. Chlamydia, another phylum of obligate intracellular parasites, contains species that can cause pneumonia, or
urinary tract infection and may be involved in coronary heart disease.[155] Finally, some species such as
Pseudomonas aeruginosa, Burkholderia cenocepacia, and Mycobacterium avium are opportunistic pathogens and
cause disease mainly in people suffering from immunosuppression or cystic fibrosis.[156] [157]
Bacteria
Bacterial infections may be treated
with antibiotics, which are classified as
bacteriocidal if they kill bacteria, or
bacteriostatic if they just prevent
bacterial growth. There are many types
of antibiotics and each class inhibits a
process that is different in the pathogen
from that found in the host. An
example of how antibiotics produce
selective toxicity are chloramphenicol
and puromycin, which inhibit the
bacterial ribosome, but not the
structurally
different
eukaryotic
[160]
ribosome.
Antibiotics are used
both in treating human disease and in
intensive farming to promote animal
growth, where they may be
contributing to the rapid development
of antibiotic resistance in bacterial
populations.[161] Infections can be
[158] [159]
Overview of bacterial infections and main species involved.
prevented by antiseptic measures such
as sterilizating the skin prior to
piercing it with the needle of a syringe, and by proper care of indwelling catheters. Surgical and dental instruments
are also sterilized to prevent contamination by bacteria. Disinfectants such as bleach are used to kill bacteria or other
pathogens on surfaces to prevent contamination and further reduce the risk of infection.
Significance in technology and industry
Bacteria, often lactic acid bacteria such as Lactobacillus and Lactococcus, in combination with yeasts and molds,
have been used for thousands of years in the preparation of fermented foods such as cheese, pickles, soy sauce,
sauerkraut, vinegar, wine and yoghurt.[162] [163]
The ability of bacteria to degrade a variety of organic compounds is remarkable and has been used in waste
processing and bioremediation. Bacteria capable of digesting the hydrocarbons in petroleum are often used to clean
up oil spills.[164] Fertilizer was added to some of the beaches in Prince William Sound in an attempt to promote the
growth of these naturally occurring bacteria after the infamous 1989 Exxon Valdez oil spill. These efforts were
effective on beaches that were not too thickly covered in oil. Bacteria are also used for the bioremediation of
industrial toxic wastes.[165] In the chemical industry, bacteria are most important in the production of
enantiomerically pure chemicals for use as pharmaceuticals or agrichemicals.[166]
Bacteria can also be used in the place of pesticides in the biological pest control. This commonly involves Bacillus
thuringiensis (also called BT), a Gram-positive, soil dwelling bacterium. Subspecies of this bacteria are used as a
Lepidopteran-specific insecticides under trade names such as Dipel and Thuricide.[167] Because of their specificity,
these pesticides are regarded as environmentally friendly, with little or no effect on humans, wildlife, pollinators and
most other beneficial insects.[168] [169]
Because of their ability to quickly grow and the relative ease with which they can be manipulated, bacteria are the
workhorses for the fields of molecular biology, genetics and biochemistry. By making mutations in bacterial DNA
and examining the resulting phenotypes, scientists can determine the function of genes, enzymes and metabolic
17
Bacteria
pathways in bacteria, then apply this knowledge to more complex organisms.[170] This aim of understanding the
biochemistry of a cell reaches its most complex expression in the synthesis of huge amounts of enzyme kinetic and
gene expression data into mathematical models of entire organisms. This is achievable in some well-studied bacteria,
with models of Escherichia coli metabolism now being produced and tested.[171] [172] This understanding of bacterial
metabolism and genetics allows the use of biotechnology to bioengineer bacteria for the production of therapeutic
proteins, such as insulin, growth factors, or antibodies.[173] [174]
See also
•
•
•
•
•
•
•
Biotechnology
Extremophiles
List of bacterial orders
Transgenic bacteria
Psychrotrophic bacteria
Microorganism
International Code of Nomenclature of Bacteria
Notes
α. The word bacteria derives from the Greek βακτήριον, baktērion, meaning "small staff".
Further reading
• Alcamo IE (2001). Fundamentals of microbiology. Boston: Jones and Bartlett. ISBN 0-7637-1067-9.
• Atlas RM (1995). Principles of microbiology. St. Louis: Mosby. ISBN 0-8016-7790-4.
• Martinko JM, Madigan MT (2005). Brock Biology of Microorganisms (11th ed.). Englewood Cliffs, N.J: Prentice
Hall. ISBN 0-13-144329-1.
• Holt JC, Bergey DH (1994). Bergey's manual of determinative bacteriology (9th ed.). Baltimore: Williams &
Wilkins. ISBN 0-683-00603-7.
• Hugenholtz P, Goebel BM, Pace NR (15 September 1998). "Impact of culture-independent studies on the
emerging phylogenetic view of bacterial diversity" [175]. J Bacteriol 180 (18): 4765–74. PMID 9733676.
PMC 107498.
• Funke BR, Tortora GJ, Case CL (2004). Microbiology: an introduction (8th ed.). San Francisco: Benjamin
Cummings. ISBN 0-8053-7614-3.
• Shively, Jessup M. (2006). Complex Intracellular Structures in Prokaryotes (Microbiology Monographs). Berlin:
Springer. ISBN 3-540-32524-7.
• Witzany G, (2008). "Bio-Communication of Bacteria and their Evolutionary Roots in Natural Genome Editing
Competences of Viruses". Open Evol J 2: 44–54. doi:10.2174/1874404400802010044.
18
Bacteria
External links
MicrobeWiki [176], an extensive wiki about bacteria [177] and viruses [178]
Bacteria which affect crops and other plants [179]
Bacterial Nomenclature Up-To-Date from DSMZ [180]
Genera of the domain Bacteria [181] - list of Prokaryotic names with Standing in Nomenclature
The largest bacteria [182]
Tree of Life: Eubacteria [183]
Videos [184] of bacteria swimming and tumbling, use of optical tweezers and other videos.
Planet of the Bacteria [185] by Stephen Jay Gould
On-line text book on bacteriology [186]
Animated guide to bacterial cell structure. [187]
Bacteria Make Major Evolutionary Shift in the Lab [188]
Cell-Cell Communication in Bacteria [189] on-line lecture by Bonnie Bassler, and TED: Discovering bacteria's
amazing communication system [190]
• Online collaboration for bacterial taxonomy. [191]
• Parts of a bacterial cell [192]
•
•
•
•
•
•
•
•
•
•
•
•
• Bacterial Chemotaxis Interactive Simulator [193] - A web-app that uses several simple algorithms to simulate
bacterial chemotaxis.
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''Escherichia coli''
27
''Escherichia coli''
Escherichia coli
Scientific classification
Domain:
Bacteria
Phylum:
Proteobacteria
Class:
Gamma Proteobacteria
Order:
Enterobacteriales
Family:
Enterobacteriaceae
Genus:
Escherichia
Species:
E. coli
Binomial name
Escherichia coli
(Migula 1895)
Castellani and Chalmers 1919
Synonyms
Bacillus coli communis Escherich 1885
Escherichia coli (commonly abbreviated E. coli; pronounced /ˌɛʃɨˈrɪkiə ˈkoʊlaɪ/, named after Theodor Escherich) is
a Gram negative rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms
(endotherms). Most E. coli strains are harmless, but some, such as serotype O157:H7, can cause serious food
poisoning in humans, and are occasionally responsible for product recalls.[1] [2] The harmless strains are part of the
normal flora of the gut, and can benefit their hosts by producing vitamin K2,[3] and by preventing the establishment
of pathogenic bacteria within the intestine.[4] [5]
E. coli are not always confined to the intestine, and their ability to survive for brief periods outside the body makes
them an ideal indicator organism to test environmental samples for fecal contamination.[6] [7] The bacteria can also
be grown easily and its genetics are comparatively simple and easily-manipulated or duplicated through a process of
metagenics, making it one of the best-studied prokaryotic model organisms, and an important species in
biotechnology and microbiology.
E. coli was discovered by German pediatrician and bacteriologist Theodor Escherich in 1885,[6] and is now classified
as part of the Enterobacteriaceae family of gamma-proteobacteria.[8]
''Escherichia coli''
28
Strains
A strain of E. coli is a sub-group within the species that has unique
characteristics that distinguish it from other E. coli strains. These
differences are often detectable only at the molecular level; however,
they may result in changes to the physiology or lifecycle of the
bacterium. For example, a strain may gain pathogenic capacity, the
ability to use a unique carbon source, the ability to take upon a
particular ecological niche or the ability to resist antimicrobial agents.
Different strains of E. coli are often host-specific, making it possible to
determine the source of fecal contamination in environmental
samples.[6] [7] For example, knowing which E. coli strains are present
in a water sample allows to make assumptions about whether the
contamination originated from a human, another mammal or a bird.
Model of successive binary fission in E. coli
New strains of E. coli evolve through the natural biological process of mutation and through horizontal gene
transfer[9] . Some strains develop traits that can be harmful to a host animal. These virulent strains typically cause a
bout of diarrhea that is unpleasant in healthy adults and is often lethal to children in the developing world.[10] More
virulent strains, such as O157:H7 cause serious illness or death in the elderly, the very young or the
immunocompromised.[4] [10]
Biology and biochemistry
E. coli is Gram-negative, facultative
anaerobic and non-sporulating. Cells
are typically rod-shaped and are about
2 micrometres (μm) long and 0.5 μm in
diameter, with a cell volume of 0.6 0.7 μm3.[11] It can live on a wide
variety of substrates. E. coli uses
mixed-acid fermentation in anaerobic
conditions,
producing
lactate,
succinate, ethanol, acetate and carbon
dioxide. Since many pathways in
mixed-acid fermentation produce
Escherichia coli cells propel themselves with flagella (long, thin structures) arranged as
hydrogen gas, these pathways require
bundles that rotate counter-clockwise, generating torque to rotate the bacterium
the levels of hydrogen to be low, as is
clockwise.
the case when E. coli lives together
with hydrogen-consuming organisms such as methanogens or sulfate-reducing bacteria.[12]
Optimal growth of E. coli occurs at 37°C (98.6°F) but some laboratory strains can multiply at temperatures of up to
49°C (120.2°F).[13] Growth can be driven by aerobic or anaerobic respiration, using a large variety of redox pairs,
including the oxidation of pyruvic acid, formic acid, hydrogen and amino acids, and the reduction of substrates such
as oxygen, nitrate, dimethyl sulfoxide and trimethylamine N-oxide.[14]
Strains that possess flagella can swim and are motile. The flagella have a peritrichous arrangement.[15]
E. coli and related bacteria possess the ability to transfer DNA via bacterial conjugation, transduction or
transformation, which allows genetic material to spread horizontally through an existing population. This process led
to the spread of the gene encoding shiga toxin from Shigella to E. coli O157:H7, carried by a bacteriophage.[16]
''Escherichia coli''
Role as normal microbiota
E. coli normally colonizes an infant's gastrointestinal tract within 40 hours of birth, arriving with food or water or
with the individuals handling the child. In the bowel, it adheres to the mucus of the large intestine. It is the primary
facultative anaerobe of the human gastrointestinal tract.[17] (Facultative anaerobes are organisms that can grow in
either the presence or absence of oxygen.) As long as these bacteria do not acquire genetic elements encoding for
virulence factors, they remain benign commensals.[18]
Therapeutic use of nonpathogenic E. coli
Nonpathogenic Escherichia coli strain Nissle 1917 also known as Mutaflor is used as a probiotic agent in medicine,
mainly for the treatment of various gastroenterological diseases,[19] including inflammatory bowel disease.[20]
Role in disease
Virulent strains of E. coli can cause gastroenteritis, urinary tract infections, and neonatal meningitis. In rarer cases,
virulent strains are also responsible for hæmolytic-uremic syndrome (HUS), peritonitis, mastitis, septicemia and
Gram-negative pneumonia.[17]
Gastrointestinal infection
Certain strains of E. coli, such as O157:H7, O121 and
O104:H21, produce potentially lethal toxins. Food
poisoning caused by E. coli is usually caused by eating
unwashed vegetables or undercooked meat. O157:H7 is
also notorious for causing serious and even
life-threatening complications like hemolytic-uremic
syndrome (HUS). This particular strain is linked to the
2006 United States E. coli outbreak of fresh spinach.
Severity of the illness varies considerably; it can be
fatal, particularly to young children, the elderly or the
immunocompromised, but is more often mild. Earlier,
poor hygienic methods of preparing meat in Scotland
Low-temperature electron micrograph of a cluster of E. coli bacteria,
killed seven people in 1996 due to E. coli poisoning,
magnified 10,000 times. Each individual bacterium is a rounded
and left hundreds more infected. E. coli can harbor both
cylinder.
heat-stable and heat-labile enterotoxins. The latter,
termed LT, contains one "A" subunit and five "B" subunits arranged into one holotoxin, and is highly similar in
structure and function to Cholera toxins. The B subunits assist in adherence and entry of the toxin into host intestinal
cells, while the A subunit is cleaved and prevents cells from absorbing water, causing diarrhea. LT is secreted by the
Type 2 secretion pathway.[21]
If E. coli bacteria escape the intestinal tract through a perforation (for example from an ulcer, a ruptured appendix, or
a surgical error) and enter the abdomen, they usually cause peritonitis that can be fatal without prompt treatment.
However, E. coli are extremely sensitive to such antibiotics as streptomycin or gentamicin. This could change since,
as noted below, E. coli quickly acquires drug resistance.[22] Recent research suggests that treatment with antibiotics
does not improve the outcome of the disease, and may in fact significantly increase the chance of developing
haemolytic uraemic syndrome.[23]
Intestinal mucosa-associated E. coli are observed in increased numbers in the inflammatory bowel diseases, Crohn's
disease and ulcerative colitis.[24] Invasive strains of E. coli exist in high numbers in the inflamed tissue, and the
number of bacteria in the inflamed regions correlates to the severity of the bowel inflammation.[25]
29
''Escherichia coli''
30
Virulence properties
Enteric E. coli (EC) are classified on the basis of serological characteristics and virulence properties.[17] Virotypes
include:
Name
Enterotoxigenic E.
coli (ETEC)
Hosts
causative agent of
diarrhea (without
fever) in humans,
pigs, sheep, goats,
cattle, dogs, and
horses
Description
ETEC uses fimbrial adhesins (projections from the bacterial cell surface) to bind enterocyte cells in
the small intestine. ETEC can produce two proteinaceous enterotoxins:
•
the larger of the two proteins, LT enterotoxin, is similar to cholera toxin in structure and
function.
•
the smaller protein, ST enterotoxin causes cGMP accumulation in the target cells and a
subsequent secretion of fluid and electrolytes into the intestinal lumen.
ETEC strains are non-invasive, and they do not leave the intestinal lumen. ETEC is the leading
bacterial cause of diarrhea in children in the developing world, as well as the most common cause of
traveler's diarrhea. Each year, ETEC causes more than 200 million cases of diarrhea and 380,000
[26]
deaths, mostly in children in developing countries.
Enteropathogenic E.
coli (EPEC)
causative agent of
diarrhea in
humans, rabbits,
dogs, cats and
horses
Like ETEC, EPEC also causes diarrhea, but the molecular mechanisms of colonization and etiology
are different. EPEC lack fimbriae, ST and LT toxins, but they utilize an adhesin known as intimin to
bind host intestinal cells. This virotype has an array of virulence factors that are similar to those
found in Shigella, and may possess a shiga toxin. Adherence to the intestinal mucosa causes a
rearrangement of actin in the host cell, causing significant deformation. EPEC cells are
moderately-invasive (i.e. they enter host cells) and elicit an inflammatory response. Changes in
intestinal cell ultrastructure due to "attachment and effacement" is likely the prime cause of diarrhea
in those afflicted with EPEC.
Enteroinvasive E.
coli (EIEC)
found only in
humans
EIEC infection causes a syndrome that is identical to Shigellosis, with profuse diarrhea and high
fever.
Enterohemorrhagic
E. coli (EHEC)
found in humans,
cattle, and goats
The most famous member of this virotype is strain O157:H7, which causes bloody diarrhea and no
fever. EHEC can cause hemolytic-uremic syndrome and sudden kidney failure. It uses bacterial
[27]
fimbriae for attachment (E. coli common pilus, ECP),
is moderately-invasive and possesses a
phage-encoded Shiga toxin that can elicit an intense inflammatory response.
Enteroaggregative E. found only in
coli (EAEC)
humans
So named because they have fimbriae which aggregate tissue culture cells, EAEC bind to the
intestinal mucosa to cause watery diarrhea without fever. EAEC are non-invasive. They produce a
hemolysin and an ST enterotoxin similar to that of ETEC.
Epidemiology of gastrointestinal infection
Transmission of pathogenic E. coli often occurs via fecal-oral transmission.[18] [28] [29] Common routes of
transmission include: unhygienic food preparation,[28] farm contamination due to manure fertilization,[30] irrigation
of crops with contaminated greywater or raw sewage,[31] feral pigs on cropland,[32] or direct consumption of
sewage-contaminated water.[33] Dairy and beef cattle are primary reservoirs of E. coli O157:H7,[34] and they can
carry it asymptomatically and shed it in their feces.[34] Food products associated with E. coli outbreaks include raw
ground beef,[35] raw seed sprouts or spinach,[30] raw milk, unpasteurized juice, unpasteurized cheese and foods
contaminated by infected food workers via fecal-oral route.[28]
According to the U.S. Food and Drug Administration, the fecal-oral cycle of transmission can be disrupted by
cooking food properly, preventing cross-contamination, instituting barriers such as gloves for food workers,
instituting health care policies so food industry employees seek treatment when they are ill, pasteurization of juice or
dairy products and proper hand washing requirements.[28]
Shiga toxin-producing E. coli (STEC), specifically serotype O157:H7, have also been transmitted by flies,[36] [37] [38]
as well as direct contact with farm animals,[39] [40] petting zoo animals,[41] and airborne particles found in
animal-rearing environments.[42]
''Escherichia coli''
Urinary tract infection
Uropathogenic E. coli (UPEC) is responsible for approximately
90% of urinary tract infections (UTI) seen in individuals with
ordinary anatomy.[17] In ascending infections, fecal bacteria
colonize the urethra and spread up the urinary tract to the bladder
as well as to the kidneys (causing pyelonephritis),[44] or the
prostate in males. Because women have a shorter urethra than
men, they are 14-times more likely to suffer from an ascending
UTI.[17]
Uropathogenic E. coli utilize P fimbriae (pyelonephritis-associated
pili) to bind urinary tract endothelial cells and colonize the
bladder. These adhesins specifically bind D-galactose-D-galactose
moieties on the P blood group antigen of erythrocytes and
E. coli bacteria, the most prevalent gram-negative flora
[43]
in the intestine.
uroepithelial cells.[17] Approximately 1% of the human population
lacks this receptor, and its presence or absence dictates an
individual's susceptibility to E. coli urinary tract infections. Uropathogenic E. coli produce alpha- and
beta-hemolysins, which cause lysis of urinary tract cells.
UPEC can evade the body's innate immune defenses (e.g. the complement system) by invading superficial umbrella
cells to form intracellular bacterial communities (IBCs).[45] They also have the ability to form K antigen, capsular
polysaccharides that contribute to biofilm formation. Biofilm-producing E. coli are recalcitrant to immune factors
and antibiotic therapy and are often responsible for chronic urinary tract infections.[46] K antigen-producing E. coli
infections are commonly found in the upper urinary tract.[17]
Descending infections, though relatively rare, occur when E. coli cells enter the upper urinary tract organs (kidneys,
bladder or ureters) from the blood stream.
Neonatal meningitis
It is produced by a serotype of Escherichia coli that contains a capsular antigen called K1. The colonisation of the
new born's intestines with these stems, that are present in the mother's vagina, lead to bacteriemia, which leads to
meningitis. And because of the absence of the igM antibodies from the mother (these do not cross the placenta
because they are too big), plus the fact that the body recognises as self the K1 antigen, as it resembles the cerebral
glicopeptides, this leads to a severe meningitis in the neonates.
Laboratory diagnosis
In stool samples microscopy will show Gram negative rods, with no particular cell arrangement. Then, either
MacConkey agar or EMB agar (or both) are inoculated with the stool. On MacConkey agar, deep red colonies are
produced as the organism is lactose positive, and fermentation of this sugar will cause the medium's pH to drop,
leading to darkening of the medium. Growth on Levine EMB agar produces black colonies with greenish-black
metallic sheen. This is diagnosic of E. coli. The organism is also lysine positive, and grows on TSI slant with a
(A/A/g+/H2S-) profile. Also, IMViC is ++-- for E. coli; as it's indol positive (red ring) and methyl red positive
(bright red), but VP negative (no change-colorless) and citrate negative (no change-green color). Tests for toxin
production can use mammalian cells in tissue culture, which are rapidly killed by shiga toxin. Although sensitive and
very specific, this method is slow and expensive.[47]
Typically diagnosis has been done by culturing on sorbitol-MacConkey medium and then using typing antiserum.
However, current latex assays and some typing antiserum have shown cross reactions with non-E. coli O157
colonies. Furthermore, not all E. coli O157 strains associated with HUS are nonsorbitol fermentors.
31
''Escherichia coli''
The Council of State and Territorial Epidemiologists recommend that clinical laboratories screen at least all bloody
stools for this pathogen. The American Gastroenterological Association Foundation (AGAF) recommended in July
1994 that all stool specimens should be routinely tested for E. coli O157:H7. It is recommended that the clinician
check with their state health department or the Centers for Disease Control and Prevention to determine which
specimens should be tested and whether the results are reportable.
Other methods for detecting E. coli O157 in stool include ELISA tests, colony immunoblots, direct
immunofluorescence microscopy of filters, as well as immunocapture techniques using magnetic beads.[48] These
assays are designed as screening tool to allow rapid testing for the presence of E. coli O157 without prior culturing
of the stool specimen.
Antibiotic therapy and resistance
Bacterial infections are usually treated with antibiotics. However, the antibiotic sensitivities of different strains of E.
coli vary widely. As Gram-negative organisms, E. coli are resistant to many antibiotics that are effective against
Gram-positive organisms. Antibiotics which may be used to treat E. coli infection include amoxicillin as well as
other semi-synthetic penicillins, many cephalosporins, carbapenems, aztreonam, trimethoprim-sulfamethoxazole,
ciprofloxacin, nitrofurantoin and the aminoglycosides.
Antibiotic resistance is a growing problem. Some of this is due to overuse of antibiotics in humans, but some of it is
probably due to the use of antibiotics as growth promoters in food of animals.[49] A study published in the journal
Science in August 2007 found that the rate of adaptative mutations in E. coli is "on the order of 10–5 per genome per
generation, which is 1,000 times as high as previous estimates," a finding which may have significance for the study
and management of bacterial antibiotic resistance.[50]
Antibiotic-resistant E. coli may also pass on the genes responsible for antibiotic resistance to other species of
bacteria, such as Staphylococcus aureus. E. coli often carry multidrug resistant plasmids and under stress readily
transfer those plasmids to other species. Indeed, E. coli is a frequent member of biofilms, where many species of
bacteria exist in close proximity to each other. This mixing of species allows E. coli strains that are piliated to accept
and transfer plasmids from and to other bacteria. Thus E. coli and the other enterobacteria are important reservoirs of
transferable antibiotic resistance.[51]
Beta-lactamase strains
Resistance to beta-lactam antibiotics has become a particular problem in recent decades, as strains of bacteria that
produce extended-spectrum beta-lactamases have become more common.[52] These beta-lactamase enzymes make
many, if not all, of the penicillins and cephalosporins ineffective as therapy. Extended-spectrum
beta-lactamase–producing E. coli are highly resistant to an array of antibiotics and infections by these strains is
difficult to treat. In many instances, only two oral antibiotics and a very limited group of intravenous antibiotics
remain effective.
Increased concern about the prevalence of this form of "superbug" in the United Kingdom has led to calls for further
monitoring and a UK-wide strategy to deal with infections and the deaths.[53] Susceptibility testing should guide
treatment in all infections in which the organism can be isolated for culture.
Phage therapy
Phage therapy—viruses that specifically target pathogenic bacteria—has been developed over the last 80 years,
primarily in the former Soviet Union, where it was used to prevent diarrhea caused by E. coli.[54] Presently, phage
therapy for humans is available only at the Phage Therapy Center in the Republic of Georgia and in Poland.[55]
However, on January 2, 2007, the United States FDA gave Omnilytics approval to apply its E. coli O157:H7 killing
phage in a mist, spray or wash on live animals that will be slaughtered for human consumption.[56] The
32
''Escherichia coli''
Bacteriophage T4 is a highly studied phage that targets E. coli for infection.
Vaccination
Researchers have actively been working to develop safe, effective vaccines to lower the worldwide incidence of E.
coli infection.[57] In March 2006, a vaccine eliciting an immune response against the E. coli O157:H7 O-specific
polysaccharide conjugated to recombinant exotoxin A of Pseudomonas aeruginosa (O157-rEPA) was reported to be
safe in children two to five years old. Previous work had already indicated that it was safe for adults.[58] A phase III
clinical trial to verify the large-scale efficacy of the treatment is planned.[58]
In 2006 Fort Dodge Animal Health (Wyeth) introduced an effective live attenuated vaccine to control airsacculitis
and peritonitis in chickens. The vaccine is a genetically modified avirulent vaccine that has demonstrated protection
against O78 and untypeable strains.[59]
In January 2007 the Canadian bio-pharmaceutical company Bioniche announced it has developed a cattle vaccine
which reduces the number of O157:H7 shed in manure by a factor of 1000, to about 1000 pathogenic bacteria per
gram of manure.[60] [61] [62]
In April 2009 a Michigan State University researcher announced that he has developed a working vaccine for a strain
of E. coli. Mahdi Saeed, professor of epidemiology and infectious disease in MSU's colleges of Veterinary Medicine
and Human Medicine, has applied for a patent for his discovery and has made contact with pharmaceutical
companies for commercial production.[63]
Role in biotechnology
Because of its long history of laboratory culture and ease of manipulation, E. coli also plays an important role in
modern biological engineering and industrial microbiology.[64] The work of Stanley Norman Cohen and Herbert
Boyer in E. coli, using plasmids and restriction enzymes to create recombinant DNA, became a foundation of
biotechnology.[65]
Considered a very versatile host for the production of heterologous proteins,[66] researchers can introduce genes into
the microbes using plasmids, allowing for the mass production of proteins in industrial fermentation processes.
Genetic systems have also been developed which allow the production of recombinant proteins using E. coli. One of
the first useful applications of recombinant DNA technology was the manipulation of E. coli to produce human
insulin.[67] Modified E. coli have been used in vaccine development, bioremediation, and production of immobilised
enzymes.[66] E. coli cannot, however, be used to produce some of the more large, complex proteins which contain
multiple disulfide bonds and, in particular, unpaired thiols, or proteins that also require post-translational
modification for activity.[64]
Studies are also being performed into programming E. coli to potentially solve complicated mathematics problems
such as the Hamiltonian path problem.[68]
Environmental quality
E. coli bacteria have been commonly found in recreational waters and their presence is used to indicate the presence
of recent fecal contamination, but E. coli presence may not be indicative of human waste. E. coli are harbored in all
warm-blooded animals: birds and mammals alike. E. coli bacteria have also been found in fish [69] and turtles. Sand
[70]
and soil [71] also harbor E. coli bacteria and some strains of E. coli have become naturalized [72]. Some
geographic areas may support unique populations of E. coli and conversely, some E. coli strains are cosmopolitan
[73].
33
''Escherichia coli''
34
Model organism
E. coli is frequently used as a model organism in
microbiology studies. Cultivated strains (e.g. E. coli
K12) are well-adapted to the laboratory environment,
and, unlike wild type strains, have lost their ability to
thrive in the intestine. Many lab strains lose their ability
to form biofilms.[74] [75] These features protect wild
type strains from antibodies and other chemical attacks,
but require a large expenditure of energy and material
resources.
In 1946, Joshua Lederberg and Edward Tatum first
described the phenomenon known as bacterial
conjugation using E. coli as a model bacterium,[76] and
it remains the primary model to study conjugation. E.
coli was an integral part of the first experiments to
understand phage genetics,[77] and early researchers,
such as Seymour Benzer, used E. coli and phage T4 to
understand the topography of gene structure.[78] Prior
to Benzer's research, it was not known whether the
gene was a linear structure, or if it had a branching pattern.
Escherichia Coli. Gram stained. The numbered ticks on the scale are
20 µM apart; the smallest, unnumbered ticks are 2 µM apart.
The long-term evolution experiments using E. coli, begun by Richard Lenski in 1988, have allowed direct
observation of major evolutionary shifts in the laboratory.[79] In this experiment, one population of E. coli
unexpectedly evolved the ability to aerobically metabolize citrate. This capacity is extremely rare in E. coli. As the
inability to grow aerobically is normally used as a diagnostic criterion with which to differentiate E. coli from other,
closely related bacteria such as Salmonella, this innovation may mark a speciation event observed in the lab.
By combining nanotechnologies with landscape ecology complex habitat landscapes can be generated with details at
the nanoscale.[80] On such synthetic ecosystems evolutionary experiments with E.coli have been performed in order
to study the spatial biophysics of adaptation in an island biogeography on-chip.
See also
•
•
•
•
•
•
•
•
•
•
Escherichia coli O157:H7
E. coli long-term evolution experiment
International Code of Nomenclature of Bacteria
T4 rII system
Bacteriological water analysis
Coliform bacteria
Contamination control
Food poisoning
Fecal coliforms
E. coli gas production from glucose video demonstration [81]
''Escherichia coli''
External links
General
•
•
•
•
•
E. coli statistics [82]
Spinach and E. coli Outbreak - U.S. FDA [83]
E. coli Outbreak From Fresh Spinach - U.S. CDC [84]
Current research on Escherichia coli at the Norwich Research Park [85]
Image of E. coli on MacConkey Agar [86]
Databases
• EcoSal [87] Continually updated Web resource based on the classic ASM Press publication Escherichia coli and
Salmonella: Cellular and Molecular Biology
• Uropathogenic Escherichia coli (UPEC) [88]
• ECODAB [89] The structure of the O-antigens that form the basis of the serological classification of E. coli
• 2DBase [90] 2D-PAGE Database of Escherichia coli University of Bielefeld - Fermentation Engineering Group
(AGFT)
• 5S rRNA Database [91] Information on nucleotide sequences of 5S rRNAs and their genes
ACLAME [92] A CLAssification of Mobile genetic Elements
AlignACE [93] Matrices that search for additional binding sites in the E. coli genomic sequence
ArrayExpress [94] Database of functional genomics experiments
ASAP [95] Comprehensive genome information for several enteric bacteria with community annotation
Bacteriome [96] E. coli DNA-Binding Site Matrices Applied to the Complete E. coli K-12 Genome
BioGPS [97] Gene portal hub
BRENDA [98] Comprehensive Enzyme Information System
BSGI [99] Bacterial Structural Genomics Initiative
CATH [100] Protein Structure Classification
CBS Genome Atlas [101]
CDD [102] Conserved Domain Database
CIBEX [103] Center for Information Biology Gene Expression Database
COGs [104]
Coli Genetic Stock Center [105] Strains and genetic information on E. coli K-12
coliBASE [106]
EcoliHub [107] - NIH-funded comprehensive data resource for E. coli K-12 and its phage, plasmids, and mobile
genetic elements
• EcoliWiki [108] is the community annotation component of EcoliHub [109]
•
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doi:10.1016/S0958-1669(00)00131-2. PMID 11024362.
[67] Tof, Ilanit (1994). "Recombinant DNA Technology in the Synthesis of Human Insulin" (http:/ / www. littletree. com. au/ dna. htm). Little
Tree Pty. Ltd.. . Retrieved 2007-11-30.
[68] "E.coli can solve math problems" (http:/ / www. deccanchronicle. com/ international/ ecoli-can-solve-math-problems-088). The Deccan
Chronicle. July 26, 2009. . Retrieved July 26, 2009.
[69] http:/ / www. d. umn. edu/ ~rhicks/ lab/ Hansen%20et%20al%202008%20JGLR%2034. pdf
[70] http:/ / pubs. acs. org/ doi/ pdf/ 10. 1021/ es0623156?cookieSet=1
[71] http:/ / www. d. umn. edu/ ~rhicks/ lab/ Ishii%20et%20al%202006%20AEM%2072. pdf
[72] http:/ / www. d. umn. edu/ ~rhicks/ lab/ Ksoll%20et%20al%202007%20AEM%2073. pdf
[73] http:/ / www. d. umn. edu/ ~rhicks/ lab/ Hansen%20et%20al%202009%20AEM%2075(6). pdf
[74] Fux CA, Shirtliff M, Stoodley P, Costerton JW (2005). "Can laboratory reference strains mirror "real-world" pathogenesis?". Trends
Microbiol. 13 (2): 58–63. doi:10.1016/j.tim.2004.11.001. PMID 15680764.
[75] Vidal O, Longin R, Prigent-Combaret C, Dorel C, Hooreman M, Lejeune P (1998). "Isolation of an Escherichia coli K-12 mutant strain able
to form biofilms on inert surfaces: involvement of a new ompR allele that increases curli expression" (http:/ / www. pubmedcentral. nih. gov/
articlerender. fcgi?tool=pmcentrez& artid=107187). J. Bacteriol. 180 (9): 2442–9. PMID 9573197. PMC 107187.
[76] Lederberg, Joshua; E.L. Tatum (October 19 1946). "Gene recombination in E. coli" (http:/ / profiles. nlm. nih. gov/ BB/ G/ A/ S/ Z/ _/
bbgasz. pdf) (PDF). Nature 158: 558. doi:10.1038/158558a0. . Source: National Library of Medicine - The Joshua Lederberg Papers (http:/ /
profiles. nlm. nih. gov/ BB/ G/ A/ S/ Z/ )
[77] "The Phage Course - Origins" (http:/ / www. cshl. edu/ History/ phagecourse. html). Cold Spring Harbor Laboratory. 2006. . Retrieved
2007-12-03.
[78] Benzer, Seymour (March 1961). "On the topography of the genetic fine structure" (http:/ / www. pubmedcentral. nih. gov/ articlerender.
fcgi?tool=pmcentrez& artid=221592). PNAS 47 (3): 403–15. doi:10.1073/pnas.47.3.403. PMC 221592.
[79] Bacteria make major evolutionary shift in the lab (http:/ / www. newscientist. com/ channel/ life/
dn14094-bacteria-make-major-evolutionary-shift-in-the-lab. html) New Scientist
[80] Keymer J.E., P. Galajda, C. Muldoon R., and R. Austin (November 2006). "Bacterial metapopulations in nanofabricated landscapes". PNAS
103 (46): 17290–295. doi:10.1073/pnas.0607971103.
[81] http:/ / www. tgw1916. net/ movies2. html
[82] http:/ / redpoll. pharmacy. ualberta. ca/ CCDB/ cgi-bin/ STAT_NEW. cgi
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[84] http:/ / www. cdc. gov/ foodborne/ ecolispinach/
[85] http:/ / www. micron. ac. uk/ organisms/ eco. html
[86] http:/ / www. microbeid. com/ Media/ mac_img. html
[87] http:/ / www. ecosal. org/
[88] http:/ / www. genome. wisc. edu/ sequencing/ upec. htm
[89] http:/ / www. casper. organ. su. se/ ECODAB/
[90] http:/ / 2dbase. techfak. uni-bielefeld. de/ cgi-bin/ 2d/ 2d. cgi
[91] http:/ / biobases. ibch. poznan. pl/ 5SData/
[92] http:/ / aclame. ulb. ac. be/
[93] http:/ / arep. med. harvard. edu/ ecoli_matrices/
38
''Escherichia coli''
[94] http:/ / www. ebi. ac. uk/ microarray-as/ ae/
[95] https:/ / asap. ahabs. wisc. edu/ asap/ home. php
[96] http:/ / www. compsysbio. org/ bacteriome/
[97] http:/ / biogps. gnf. org/ #goto=welcome
[98] http:/ / www. brenda-enzymes. info/
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[103] http:/ / cibex. nig. ac. jp/ index. jsp
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[105] http:/ / cgsc. biology. yale. edu/ index. php
[106] http:/ / xbase. bham. ac. uk/ colibase/
[107] http:/ / ecolihub. org
[108] http:/ / ecoliwiki. net
[109] http:/ / www. ecolihub. org
39
Salmonellosis
40
Salmonellosis
Salmonellosis
Classification and external resources
ICD-10
A 02.0
ICD-9
003.0
[1]
[2]
Salmonellosis is an infection with Salmonella bacteria. Most people who get infected with Salmonella develop
diarrhea, fever, vomiting, and abdominal cramps, 8 to 72 hours after infection. In most cases, the illness lasts 4 to 7
days; most affected persons recover without treatment.[3] However, in some persons the diarrhea may be so severe
that the patient becomes dangerously dehydrated, and must be taken to a hospital. At the hospital, the patients may
receive intravenous fluids to treat their dehydration, and medications may be given to provide symptomatic relief,
like fever reduction. In severe cases, the Salmonella infection may spread from the intestines to the blood stream,
and then to other body sites, and can cause death unless the person is treated promptly with antibiotics. The elderly,
infants, and those with impaired immune systems are more likely to have a severe illness. Some people afflicted with
salmonellosis later experience reactive arthritis, which can have long-lasting, disabling effects.
The type of Salmonella usually associated with infections in humans is called nontyphoidal Salmonella. It is usually
contracted from sources such as:
•
•
•
•
•
Poultry, pork, and cattle, if the meat is prepared incorrectly or somehow becomes infected with the bacteria.[4]
Infected eggs and milk, as well as egg products, when not prepared, handled, or refrigerated properly.[4]
Reptiles such as turtles, lizards, and snakes, as they can carry the bacteria on their skin.
Pet rodents
Tainted fruits and vegetables[4]
A rarer form of Salmonella called typhoidal Salmonella can lead to typhoid fever. It is only carried by humans, and
is usually contracted through direct contact with the fecal matter of an infected person. It therefore mainly occurs in
countries that do not have advanced systems for handling human waste.
Etymology
Both Salmonellosis and the Salmonella genus of microorganisms derive their names from a modern Latin coining
after Daniel E. Salmon (1850–1914), an American veterinary surgeon. He had help from Theobald Smith, and
together they found the bacterium in pigs.
Symptoms
The bacterium induces responses in the animal that it is infecting, and this is what typically causes the symptoms,
rather than any direct toxin produced. Symptoms are usually gastrointestinal, including nausea, vomiting, abdominal
cramps and bloody diarrhea with mucus. Headache, fatigue and rose spots are also possible. These symptoms can be
severe, especially in young children and the elderly. Symptoms last generally up to a week, and can appear 12 to 72
hours after ingesting the bacterium.
After bacterial infections, reactive arthritis (a.k.a. Reiters syndrome) can develop.[5] In sickle-cell anemia,
osteomyelitis due to Salmonella infection is much more common than in the general population. Note however,
salmonella infection is more frequently the cause of osteomyelitis in sickle-cell anemia patients, not the most
common cause. The most common cause of osteomyelitis remains due to Staphylococcus infection.
Salmonellosis
Incidents of salmonellosis
About 142,000 Americans are infected each year with Salmonella enteritidis from chicken eggs, and about 30 die.[6]
Up to 2005
The U.S. Government reported that as many as 20% of all chickens were contaminated with Salmonella in the late
1990s, and 16.3% were contaminated in 2005.[7] In the mid to late twentieth century, Salmonella enterica serovar
Enteritidis was a common contaminant of eggs. This is much less common now with the advent of hygiene measures
in egg production, and the vaccination of laying hens to prevent Salmonella colonization. Many different Salmonella
serovars also cause severe diseases in animals other than human beings.
2006
In June 2006, the BBC reported that the Cadbury chocolate manufacturer withdrew a number of products when
products contaminated with Salmonella resulted in up to 56 cases of salmonellosis.[8] The causes had been traced to
a leaking pipe at a Cadbury plant in Herefordshire in January 2006, though the announcement was not made until
June.
2007
In February 2007, the U.S. Food and Drug Administration (FDA) issued a warning to consumers not to eat certain
jars of Peter Pan peanut butter or Great Value peanut butter, due to risk of contamination with S. Tennessee. [9]
In March 2007, around 150 people were diagnosed with salmonellosis after eating tainted food at a governor's
reception in Krasnoyarsk, Russia. Over 1,500 people attended the ball on March 1, and fell ill as a consequence of
ingesting salmonella-tainted sandwiches.
About 150 people were sickened by salmonella-tainted chocolate cake produced by a major bakery chain in
Singapore in December 2007. [10]
2008
From April 10, 2008 to July 8, 2008, the rare Saintpaul serotype of Salmonella enterica caused at least 1017 cases of
salmonellosis food poisoning in 41 states throughout the United States, the District of Columbia, and Canada. As of
July 2008, the U.S. Food and Drug Administration suspects that the contaminated food product is a common
ingredient in fresh salsa, such as raw tomato, fresh jalapeño pepper, fresh serrano pepper, and fresh cilantro. It is the
largest reported salmonellosis outbreak in the United States since 1985. New Mexico and Texas have been
proportionally the hardest hit by far, with 49.7 and 16.1 reported cases per million, respectively. The greatest number
of reported cases have occurred in Texas (384 reported cases), New Mexico (98), Illinois (100), and Arizona (49).[11]
There have been at least 203 reported hospitalizations linked to the outbreak, it has caused at least one death, and it
may have been a contributing factor in at least one additional death.[12] The CDC maintains that "it is likely many
more illnesses have occurred than those reported." If applying a previous CDC estimated ratio of non-reported
salmonellosis cases to reported cases (38.6:1), one would arrive at an estimated 40,273 illnesses from this
outbreak.[13]
As of 18 July 2008, the FDA removed raw tomatoes and cilantro as potential carriers; however, fresh jalapeño
peppers and fresh serrano peppers still remain.[14]
In December 2008 and January 2009, several Midwestern states, including Ohio (officially confirmed by state
authorities), reported an outbreak of salmonellosis from Salmonella typhimurium that had sickened at least 50
people, due to contaminated dairy products like cheeses.
41
Salmonellosis
2009
On January 17, 2009, the FDA announced they had traced the source of an outbreak of Salmonella typhimurium to a
plant in Blakely, Georgia, owned by Peanut Corporation of America (PCA), and urged people to postpone eating
commercially-prepared or manufactured peanut butter-containing products and institutionally-served peanut
butter.[15] Salmonella was reported to be found in 46 states in the United States in at least 3,862 peanut butter-based
products such as crackers, energy bars, and peanut butter cookies from at least 343 food companies. Dog treats were
affected as well. At least 691 people in more than 46 states became sick, and the Salmonella claimed at least nine
lives as of March 25.[16] [17] [18] [19] [20]
Peanut butter and peanut paste manufactured by PCA were distributed to hundreds of firms for use as an ingredient
in thousands of different products, such as cookies, crackers, cereal, candy and ice cream, all of which were recalled.
Some products were also sold directly to consumers in retail outlets like dollar stores.[15]
On March 14, 2009, expressing his own personal concern for the safety of his children who enjoy peanut butter,
President Obama announced the establishment of the Food Safety Working Group, "an interagency effort to help
overhaul the oversight system." [21] The announcement came days after the FDA, also responding, released its first
"guidance" on dealing with Salmonella contamination.
Four-Inch Regulation
The "Four-Inch Regulation" or "Four-Inch Law" is a colloquial name for a regulation issued by the U.S. Food and
Drug Administration in 1975, restricting the sale of turtles with a carapace length of less than four inches.
Exceptions are provided for scientific and educational use, export, and private sale.[22]
The regulation was promulgated, according to the FDA, "because of the public health impact of turtle-associated
salmonellosis". There had been reported cases of young children placing small turtles in their mouths, which led to
the size-based restriction.
Prevention
The FDA has published guidelines[23] to help reduce the chance of food-borne salmonellosis. Food must be cooked
to 68–72°C (145–160°F) and liquids like soups or gravies must be boiled. Freezing kills some Salmonella, but it is
not sufficient to reliably reduce Salmonella below infectious levels. While Salmonella is usually heat-sensitive, it
does acquire heat resistance in high-fat environments such as peanut butter.[24]
Antibodies and vaccine development
Salmonella antibodies were first found in Malawi children in research published in 2008. The Malawian researchers
have identified an antibody that protects children against bacterial infections of the blood caused by Salmonella. A
study of 352 children at Blantyre's Queen Elizabeth hospital found that children up to two years old develop
antibodies that aid in killing the bacteria. The researchers proposed that this could lead to a possible Salmonella
vaccine.[25]
42
Salmonellosis
See also
• 1984 Rajneeshee bioterror attack
• Typhoid fever
• List of foodborne illness outbreaks
External links
• CDC website, Division of Bacterial and Mycotic Diseases, Disease Listing: Salmonellosis [26]
• CFIA Website: Salmonellae [27]
• Protective salmonella antibodies found in Malawi children, Sub-Saharan Africa gateway, Science and
Development Network, [28]
References
[1]
[2]
[3]
[4]
http:/ / apps. who. int/ classifications/ apps/ icd/ icd10online/ ?ga00. htm+ a020
http:/ / www. icd9data. com/ getICD9Code. ashx?icd9=003. 0
http:/ / www. fsis. usda. gov/ factsheets/ salmonella_questions_& _answers/ index. asp#3
"FDA/CFSAN - Food Safety A to Z Reference Guide - Salmonella" (http:/ / www. cfsan. fda. gov/ ~dms/ a2z-s. html). FDA - Center for
Food Safety and Applied Nutrition. 2008-07-03. . Retrieved 2009-02-14.
[5] Dworkin MS, Shoemaker PC, Goldoft MJ, Kobayashi JM (2001). "Reactive arthritis and Reiter's syndrome following an outbreak of
gastroenteritis caused by Salmonella enteritidis". Clin Infect Dis 33 (7): 1010–14. doi:10.1086/322644. PMID 11528573.
[6] "Administration Urged to Boost Food Safety Efforts" (http:/ / www. washingtonpost. com/ wp-dyn/ content/ article/ 2009/ 07/ 07/
AR2009070702343. html?hpid=topnews). Washington Post. 2009. . Retrieved 2009-07-07. "Among them is a final rule, issued by the FDA, to
reduce the contamination in eggs. About 142,000 Americans are infected each year with Salmonella enteritidis from eggs, the result of an
infected hen passing along the bacterium. About 30 die."
[7] Burros, Marian (March 8, 2006). "More Salmonella Is Reported in Chickens" (http:/ / www. nytimes. com/ 2006/ 03/ 08/ dining/ 08well.
html?ex=1179288000& en=1f7944fcd0d6fc64& ei=5070). The New York Times. . Retrieved 2007-05-13.
[8] "Cadbury named over salmonella outbreak" (http:/ / www. guardian. co. uk/ food/ Story/ 0,,1826262,00. html). Guardian Unlimited.
2006-07-21. . Retrieved 2007-09-09.
[9] http:/ / www. fda. gov/ bbs/ topics/ NEWS/ 2007/ NEW01563. html
[10] http:/ / www. channelnewsasia. com/ stories/ singaporelocalnews/ view/ 316110/ 1/ . html
[11] "Cases infected with the outbreak strain of Salmonella Saintpaul, United States, by state" (http:/ / www. cdc. gov/ salmonella/ saintpaul/
map. html). . For some states, such as California, the CDC has recently revised the tally of identified illness downward.
[12] August 8, 2008: Investigation of Outbreak of Infections Caused by Salmonella Saintpaul | Salmonella CDC (http:/ / www. cdc. gov/
salmonella/ saintpaul/ )
[13] Voetsch, et al. (2004-04-15). "FoodNet Estimate of the Burden of Illness Caused by Nontyphoidal Salmonella Infections in the United
States" (http:/ / www. journals. uchicago. edu/ doi/ full/ 10. 1086/ 381578). Clinical Infectious Diseases, 2004; 38:S3. .
[14] Elizabeth Landau (2008-07-18). "FDA lifts warning on tomatoes" (http:/ / www. cnn. com/ 2008/ HEALTH/ conditions/ 07/ 17/ fda.
salmonella/ index. html). .
[15] Recall of Products Containing Peanut Butter: Salmonella Typhimurium (http:/ / www. fda. gov/ oc/ opacom/ hottopics/ salmonellatyph.
html), U.S. Food and Drug Administration.
[16] Recall of Peanut-Containing Products: Salmonella Typhimurium (Current Update) (http:/ / www. fda. gov/ oc/ opacom/ hottopics/
salmonellatyph. html), U.S. Food and Drug Administration
[17] Investigation Update: Outbreak of Salmonella Typhimurium Infections, 2008–2009 (http:/ / www. cdc. gov/ salmonella/ typhimurium/
update. html), Centers for Disease Control and Prevention
[18] http:/ / www. reuters. com/ article/ newsOne/ idUSTRE50F7GH20090119
[19] MSNBC: http:/ / www. msnbc. msn. com/ id/ 28749159
[20] http:/ / www. nytimes. com/ 2009/ 01/ 27/ health/ 27peanuts. html?ref=health
[21] Weise, Elizabeth (March 2009). Salmonella outbreaks lead to food-safety changes (http:/ / www. usatoday. com/ news/ health/
2009-04-01-nuts-salmonella-food-safety_N. htm). .
[22] "Human Health Hazards Associated with Turtles" (http:/ / www. fda. gov/ cvm/ turtlereg. htm). U.S. Food and Drug Administration. .
Retrieved 2007-06-29.
[23] "Salmonella Questions and Answers" (http:/ / www. fsis. usda. gov/ Fact_Sheets/ Salmonella_Questions_& _Answers/ index. asp). USDA
Food Safety and Inspection Service. 2006-09-20. . Retrieved 2009-01-21.
[24] http:/ / www. reuters. com/ article/ healthNews/ idUSTRE5296H420090310
43
Salmonellosis
[25] MacLennan CA, Gondwe EN, Msefula CL, et al. (April 2008). "The neglected role of antibody in protection against bacteremia caused by
nontyphoidal strains of Salmonella in African children" (http:/ / www. jci. org/ articles/ view/ 33998). J. Clin. Invest. 118 (4): 1553–62.
doi:10.1172/JCI33998. PMID 18357343. PMC 2268878. .
[26] http:/ / www. cdc. gov/ nczved/ dfbmd/ disease_listing/ salmonellosis_gi. html
[27] http:/ / www. inspection. gc. ca/ english/ fssa/ concen/ cause/ salmonellae. shtml
[28] http:/ / www. scidev. net/ en/ sub-suharan-africa/ news/ sub-saharan-africa-news-in-brief-13-25-march. html
44
''Clostridium perfringens''
45
''Clostridium perfringens''
Clostridium perfringens
Photomicrograph of gram-positive Clostridium perfringens
bacilli.
Scientific classification
Kingdom:
Bacteria
Division:
Firmicutes
Class:
Clostridia
Order:
Clostridiales
Family:
Clostridiaceae
Genus:
Clostridium
Species:
perfringens
Binomial name
Clostridium perfringens
Veillon & Zuber 1898
Hauduroy et al. 1937
Clostridium perfringens (formerly known as C. welchii) is a Gram-positive, rod-shaped, anaerobic, spore-forming
bacterium of the genus Clostridium.[1] C. perfringens is ubiquitous in nature and can be found as a normal
component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates, insects, and
soil.
Infection characteristics
Clostridium perfringens is commonly encountered in infections as a benign component of the normal flora.[2] In this
case, its role in disease is minor.
Infections due to C. perfringens show evidence of tissue necrosis, bacteremia, emphysematous cholecystitis, and gas
gangrene, which is also known as clostridial myonecrosis. The toxin involved in gas gangrene is known as α-toxin,
which inserts into the plasma membrane of cells, producing gaps in the membrane that disrupt normal cellular
function.[3]
After ingestion, bacteria multiply and lead to colic, diarrhea, and sometimes nausea.
The action of C. perfringens on dead bodies is known to mortuary workers as tissue gas and can be halted only by
embalming.
''Clostridium perfringens''
Food poisoning
In the United Kingdom and United States, C. perfringens bacteria are the third-most-common cause of food-borne
illness, with poorly prepared meat and poultry the main culprits in harboring the bacterium.[3] The Clostridium
perfringens enterotoxin (CPE) mediating the disease is heat-labile (dies at 74 °C) and can be detected in
contaminated food, if not heated properly, and feces .[4]
Incubation time is between 6 and 24 (commonly 10-12) hours after ingestion of contaminated food. Often, meat is
well prepared but too far in advance of consumption. Since C. perfringens forms spores that can withstand cooking
temperatures, if let stand for long enough, germination ensues and infective bacterial colonies develop. Symptoms
typically include abdominal cramping and diarrhea; vomiting and fever are unusual. The whole course usually
resolves within 24 hours. Very rare, fatal cases of clostridial necrotizing enteritis (also known as Pig-Bel) have been
known to involve "Type C" strains of the organism, which produce a potently ulcerative β-toxin. This strain is most
frequently encountered in Papua New Guinea.
It is likely that many cases of C. perfringens food poisoning remain subclinical, as antibodies to the toxin are
common among the population. This has led to the conclusion that most of the population has experienced food
poisoning due to C. perfringens.[]
Gas gangrene
Clostridium perfringens is the most common bacterial agent for Gas gangrene.
• Gangrene is necrosis and putrefaction of tissues. Gas production forms bubbles of gas in muscle (crepitus) and
smell in decomposing tissue.
• After rapid and destructive local spread (which can take hours), systemic spread of bacteria and bacterial toxins
may result in death. This is a problem in major trauma and in military contexts.
• Gram-positive spore can form anaerobic bacilli
• It is a saprophyte, meaning it occurs in soil, H2O, decomposing plant, human and animal feces
• Under appropriate conditions, spores can reactivate into a vegetative cell
• Can grow in anaerobic dead tissue or dirt. Produces cytotoxin that kills cells.
• Traumatic wounds should be cleaned. Wounds that cannot be cleaned should not be stitched shut.
• Spores can withstand boiling water. Autoclaving is necessary to ensure sterility.
• Penicillin prophylaxis kills clostridia, and is thus useful for dirty wounds and lower leg amputations
• If detected on clinical grounds, should not wait for lab results
• If adrenalin used for injection is contaminated with spores, catastrophic reactions can result.
• Prompt and adequate surgical attention is of paramount importance
• Grows readily on blood agar plate in anaerobic conditions and often produces a zone of hemolysis
• Growth in food can produce toxins causing acute, self-limiting diarrhea
• High infectious dose is required; carrier state persists for several days
46
''Clostridium perfringens''
47
Colony characteristics
On blood agar plates, C. perfringens grown anaerobically
produces β-haemolytic, flat, spreading, rough, translucent
colonies with irregular margins. A Nagler agar plate,
containing 5-10% egg yolk, is used to identify strains that
produce α-toxin, a diffusible lecithinase that interacts
with the lipids in egg yolk to produce a characteristic
precipitate around the colonies. One-half of the plate is
inoculated with antitoxin to act as a control in the
identification.
External links
• Pathema-Clostridium Resource [5]
C. perfringens colonies on an egg yolk agar plate showing a white
precipitate
References
[1] Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
[2] Wells CL, Wilkins TD (1996). Clostridia: Sporeforming Anaerobic Bacilli. In: Barron's Medical Microbiology (Barron S et al., eds.) (4th
ed.). Univ of Texas Medical Branch. (via NCBI Bookshelf) (http:/ / www. ncbi. nlm. nih. gov/ books/ bv. fcgi?rid=mmed. section. 1131) ISBN
0-9631172-1-1.
[3] Warrell et al. (2003). Oxford Textbook of Medicine (4th ed.). Oxford University Press. ISBN 0-19-262922-0.
[4] Murray et al. (2009). Medical Microbiology (6th ed.). Mosby Elsevier. ISBN 978-0-323-05470-6.
[5] http:/ / pathema. jcvi. org/ cgi-bin/ Clostridium/ PathemaHomePage. cgi
Article Sources and Contributors
Article Sources and Contributors
Bacteria Source: http://en.wikipedia.org/w/index.php?oldid=358510842 Contributors: (jarbarf), 0, 0ceans11, 12josh21, 168..., 217.99.96.xxx, A Softer Answer, A.R., AKGhetto, Ace ETP,
Adenosine, AgentCDE, Ahoerstemeier, Ajsh, AkaDada, Alanmcleod, Alesnormales, Alexander Mclean, Alexbbard, Alext2007, AlphaEta, Alphax, Alsandro, Alucard (Dr.), Amir beckham,
Amorymeltzer, Anaraug, Anclation, Andefs, Andre Engels, Andrew Levine, Andrewpmk, AndyZ, Angela, Anonymous editor, Another Matt, Antandrus, Anthere, Anthony717, Antiuser,
Arcadian, Arman88, Artichoker, Ashishbhatnagar72, Ashley Y, Atomicskier, Aude, Avaragado, AxelBoldt, Az1568, AzaToth, Azaroonus, Azhyd, B.j.boomsma, Babalaki, Bact, Badagnani,
Baffclan, Bart133, Beaumont, Beetstra, Bemoeial, Bendzh, Bensaccount, Bhadani, Biophys, Bob Blaylock, Bobblewik, Bobo192, Bogdangiusca, Boredom inc., BorgQueen, BostonMA, Bozartas,
Brian0918, Brighterorange, BrownHairedGirl, Brudersohn, Bubba hotep, Bushcarrot, Busydude, CALR, CWY2190, Cacycle, Cailil, Can't sleep, clown will eat me, Capricorn42, Carabinieri,
Carbon-16, CaseInPoint, Cd108, CelticJobber, Ceramic2metal, Ceyockey, Chaos, CharlotteWebb, Chcknwnm, Cheaprug, Chizeng, Chooper, Chris 73, Chris Capoccia, ChrisO, Chrislk02,
Christopher Parham, Christopherkgreer, Cimex, Clarkzz1234, Clay70, Clemwang, ClockworkSoul, Cohesion, Colby Peterson, Colfer2, CommonsDelinker, Conversion script, Crowded Mouth,
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Image Sources, Licenses and Contributors
Image Sources, Licenses and Contributors
file:EscherichiaColi NIAID.jpg Source: http://en.wikipedia.org/w/index.php?title=File:EscherichiaColi_NIAID.jpg License: unknown Contributors: Credit: Rocky Mountain Laboratories,
NIAID, NIH
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Image:Antoni van Leeuwenhoek.png Source: http://en.wikipedia.org/w/index.php?title=File:Antoni_van_Leeuwenhoek.png License: Public Domain Contributors: J. Verkolje
Image:Bacterial morphology diagram.svg Source: http://en.wikipedia.org/w/index.php?title=File:Bacterial_morphology_diagram.svg License: Public Domain Contributors: user:LadyofHats
Image:Relative scale.svg Source: http://en.wikipedia.org/w/index.php?title=File:Relative_scale.svg License: Public Domain Contributors: User:Fvasconcellos
Image:Average prokaryote cell- en.svg Source: http://en.wikipedia.org/w/index.php?title=File:Average_prokaryote_cell-_en.svg License: Public Domain Contributors: User:LadyofHats
Image:Carboxysome 3 images.png Source: http://en.wikipedia.org/w/index.php?title=File:Carboxysome_3_images.png License: Creative Commons Attribution 3.0 Contributors: Prof. Todd
O. Yeates, UCLA Dept. of Chem. and Biochem.
Image:EMpylori.jpg Source: http://en.wikipedia.org/w/index.php?title=File:EMpylori.jpg License: unknown Contributors: Yutaka Tsutsumi, M.D. Professor Department of Pathology Fujita
Health University School of Medicine
Image:Gram Stain Anthrax.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Gram_Stain_Anthrax.jpg License: Public Domain Contributors: DO11.10, Dark journey, Ewen, NEON
ja, Yuval Madar
Image:Bluegreen algae.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Bluegreen_algae.jpg License: Public Domain Contributors: Original uploader was TimVickers at
en.wikipedia
Image:Binary fission anim.gif Source: http://en.wikipedia.org/w/index.php?title=File:Binary_fission_anim.gif License: unknown Contributors: User:ZabMilenko
Image:Growing colony of E. coli.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Growing_colony_of_E._coli.jpg License: GNU Free Documentation License Contributors: Stewart
EJ, Madden R, Paul G, Taddei F
Image:Flagellum base diagram en.svg Source: http://en.wikipedia.org/w/index.php?title=File:Flagellum_base_diagram_en.svg License: Public Domain Contributors: User:LadyofHats
Image:Streptococcus mutans Gram.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Streptococcus_mutans_Gram.jpg License: Creative Commons Attribution-Sharealike 2.5
Contributors: Y tambe
Image:Collapsed_tree_labels_simplified.png Source: http://en.wikipedia.org/w/index.php?title=File:Collapsed_tree_labels_simplified.png License: Public Domain Contributors: Original
uploader was TimVickers at en.wikipedia
Image:SalmonellaNIAID.jpg Source: http://en.wikipedia.org/w/index.php?title=File:SalmonellaNIAID.jpg License: unknown Contributors: Cecil, Copydays, Dark journey, Gammy, Muriel
Gottrop, NEON ja, Smooth O, Taragui, 2 anonymous edits
File:Bacterial infections and involved species.png Source: http://en.wikipedia.org/w/index.php?title=File:Bacterial_infections_and_involved_species.png License: Public Domain
Contributors: Mikael Häggström
Image:Life cycle of Escherichia coli.png Source: http://en.wikipedia.org/w/index.php?title=File:Life_cycle_of_Escherichia_coli.png License: unknown Contributors: See original article.
Original source file converted to with and optimized with by .
Image:Ecoli flagellum.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Ecoli_flagellum.jpg License: Public Domain Contributors: Nicolle Rager Fuller, National Science Foundation
Image:E coli at 10000x, original.jpg Source: http://en.wikipedia.org/w/index.php?title=File:E_coli_at_10000x,_original.jpg License: Public Domain Contributors: Photo by Eric Erbe, digital
colorization by Christopher Pooley, both of USDA, ARS, EMU.
File:E choli Gram.JPG Source: http://en.wikipedia.org/w/index.php?title=File:E_choli_Gram.JPG License: GNU Free Documentation License Contributors: User:Bobjgalindo
File:20100117 0048SS EscherichiaColi.jpg Source: http://en.wikipedia.org/w/index.php?title=File:20100117_0048SS_EscherichiaColi.jpg License: GNU Free Documentation License
Contributors: Bob Blaylock
file:Clostridium_perfringens.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Clostridium_perfringens.jpg License: Public Domain Contributors: Content Providers(s): CDC/Don
Stalons
Image:Clostridium perfringens 01.png Source: http://en.wikipedia.org/w/index.php?title=File:Clostridium_perfringens_01.png License: Public Domain Contributors: Photo Credit: Content
Providers(s): CDC/Dr. Stuart E. Starr
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License
License
Creative Commons Attribution-Share Alike 3.0 Unported
http:/ / creativecommons. org/ licenses/ by-sa/ 3. 0/
51