Download Chapter 1 Introduction to Microbiology

Unit 1
Chapter 1
Bacterial Cell Structure
CLS 3303
Clinical Microbiology
Taxonomy
 Defined as the orderly classification & grouping of organisms into
categories
 Kingdom, Division, Class, Order, Family, Tribe, Genus and
Species ( these are the formal levels of classification)
 Family = “Clan”; has “–aceae” ending
 Genus = “Human last name”
 Species = “Human first name”
 When in print, genus and species are italicized. (Staphylococcus
aureus)
 , When written genus and species are underlined.
(Staphylococcus aureus)
 To abbreviate organism names: use first letter
capitalized of the genus followed by a period and the
species epithet. ( i.e S. aureus)
Nomenclature
 Staphylococcus sp. is used when referring to the genus as
a whole when the species is not identified.
 “sp.” – singular (Staphylococcus sp.)
 “spp.” – plural (Staphylococcus spp.)
Classification by Cellular Type
 Bacteria Identification – test each bacterial culture for a
variety of metabolic characteristics and compare the results
with known results.
 All organisms are either “prokaryotes”, “eukaryotes”, or
“archaeobacteria”
Classification by Cellular Type: Prokaryotes
 PROKARYOTES - bacteria
 Do not have a membranebound nucleus
 DNA is a single circular
chromosome and RNA are
free in the cytoplasm
 Have both cell (plasma)
membrane AND cell wall.
 Have no mitochondria,
endoplasmic reticulum
(ER) or Golgi bodies
Classification by Cellular Type: Eukaryotes
 EUKARYOTES - fungi,
algae, protozoa, animal
cells, and plant cells
 Cells have nuclei that
contains DNA and are
complex
 Most cells do NOT have
a cell wall (Fungi have
cell walls made chitin)
Classification by Cellular Type:
Archaeobacteria
 Resembles eukaryotes
 Found in microorganisms that grow under extreme
environmental conditions
 Cell wall lacks peptidoglycan
 See chart on page 5 for comparisons of Prokaryotes and
Eurkaryotes
Prokaryotic & Eukaryotic Cell Comparison
Bacterial Cell Wall
Gram Positive (G+) Cell Wall
 Very thick protective peptidoglycan layer
 Many G+ antibiotics act by preventing synthesis of
peptidoglycan
 Consists of cross-linked chains of glycan
 Also contain teichoic acid and lipoteichoic acid
 Unique structure makes these bacteria G+ by protecting
against the decolorizing step in Gram staining
Gram Negative (G-) Cell Wall
 Two layers; outer is much thinner than G+ cell walls
 Outer wall contains several molecules, including Lipid A
which is responsible for producing fever and shock in
infections with G- bacteria
 The thin walls allow the decolorizer to enter the cell and
take out the crystal violet stain.
(G+) and (G-) Microorganisms
 G+ cocci in clusters→
 G- bacilli (rods)→
 When identifying bacteria, remember that
rods can sometimes be short and look
like cocci, but cocci do not look like rods
Acid Fast Cell Wall
 Mainly Mycobacteria and Nocardia
 Have a G+ cell wall structure but also a waxy layer of
glycolipids and fatty acids (mycolic acid). It is hydrophobic
and affects permeability
 Waxy layer makes them difficult to gram stain (More than
60% of the cell wall is lipid)
 Cannot be decolorized by acid-alcohol, hence the name
“acid fast”
 Bacteria is pink
 Background is green or blue
Absence of Cell Wall
 Mainly Mycoplasma and Ureaplasma
 Lack of cell wall results in a variety of shapes
microscopically
 Contain sterols in cell membrane
Surface Polymers: Slime Layers
 Some bacteria produce slime layers
 Made of polysaccharides
 Inhibit phagocytosis and also help to attach to the
host.
Surface Polymers: Capsule
 Some bacteria produce a
capsule
 Protect the bacteria
from phagocytosis
 Capsule usually does
not stain, but can
appear as a clear area
(halo-like)
Cell Appendages
 Flagella – exterior protein filaments that rotate and
cause bacteria to be motile
 Polar
– Extend from one end
– Can occur singly or in multiple tufts
 Peritrichous
– Flagella found on all sides of bacteria
 Pili (fimbriae) – hairlike projections that aid in
attachment to surfaces
Examples of Flagella
Bacterial Morphology
 Microscopic Shapes
 Cocci (spherical)
 Bacilli (rod-shaped)
 Spirochetes (helical)
 Groupings
 Singly
 Pairs
 Clusters
 Chains
 Palisading
Bacterial Morphology (cont’d)
 Size and length
 Short
 Long
 Filamentous:
 Fusiform: bacilli with tapered, pointed ends
 Curved
 Pleomorphic: variance in size & shape within a pure
culture
Other Common Bacterial Stains:
Acridine Orange (fluorochrome dye)
 Stains nucleic acid of
both G+ and G- bacteria,
either living or dead;
used to locate bacteria in
blood cultures and other
specimens where
background material
obscures gram stains
Other Common Bacterial Stains:
Methylene Blue
 Stain for Corynebacterium diphtheriae to show
metachromatic granules and as counter-stain in acid-fast
stain procedures
Other Common Bacterial Stains: Lactophenol
Cotton Blue – fungal stain
Other Common Bacterial Stains:
Calcuflour White – fungal stain
 A fluorochrome that
binds to chitin in
fungal cell walls
 Apple-green or bluewhite with a
fluorescent
microscope
Other Common Bacterial Stains: India Ink
 Negative stain for capsules, surrounds certain yeasts
Other Common Bacterial Stains:
Endospore stain
 Heat is used to help
the primary stain
(Malachite green)
into the spore. The
spore stains green
 The counter stain,
(safranin) stains the
rest of the organism
Microbial Growth and Nutrition Needs
 Source of carbon for making cellular constituents
 Source of nitrogen for making proteins
 Source of energy (ATP) for cellular functions
 Smaller amounts of other molecules
Nutritional Requirements for Growth
 Autotrophs (lithotrophs)
 Able to grow simply, using only CO2, water and inorganic
salts
 Obtain energy via photosynthesis or oxidation of
inorganic compounds
 Occur in nature and do not normally cause disease
Nutritional Requirements for Growth
 Heterotrophic
 Require more complex substances for growth
 Require an organic source of carbon and obtain energy
by oxidizing or fermenting organic substances
 All human bacteria fall in this category
 Within this group, nutritional needs vary greatly
Types of Growth Media
 Minimal medium – simple; not usually used in
diagnostic clinical microbiology
 Nutrient medium – made of extracts of meat or soy
beans
 Enriched medium – nutrient medium with extra growth
factors, such as blood
 Selective medium – contains additives that inhibit the
growth of some bacteria while allowing others to grow
 Differential medium – contains additives that allow
visualization of metabolic differences in bacteria
 Transport medium – holding medium to preserve
those bacteria present but does not allow multiplication
Environmental Factors Influencing Growth
 pH – most media is between 7.0 and 7.5
 Temperature – most pathogens grow at body
temperature; grown at 35° C in the lab
Environmental Factors Influencing Growth
 Gaseous composition
 Obligate aerobes – require oxygen
 Obligate anaerobes – cannot grow in the presence
of oxygen
 Facultative anaerobes – can grow with or
without oxygen
 Capnophilic – grow better with extra CO2 (5 -10%)
 Microaerophilic- grow better in low oxygen
environments ( about 20%)
 Campylobacter spp. require 5 – 6% oxygen
Bacterial Growth
 Reproduce by binary fission
 Can be fast (as little as 20 minutes for E. coli) or slow (as
long as 24 hours for M. tuberculosis)
Determination of the Number of bacterial cells
 Direct counting under microscope: estimate the number of
bacteria in a specimen. Does not distinguish live or dead
cells
 Direct plate count: grown from dilutions of broth cultures.
Counts viable cells only. Colony Forming Units (CFU/mL)
 Density measurement: (turbidity) bacterial broth culture in
log phase
Bacterial Biochemistry and Metabolism
 Metabolic reactions cause production of energy in form
of ATP
 Identification systems analyze unknown specimens for:
 Utilization of variety of substances as a source of carbon
 Production of specific end products from various
substrates
 Production of acid or alkaline pH in the test medium
Fermentation
 Anaerobic process in obligate and facultative
anaerobes
 The electron acceptor is an organic compound
 Does NOT require oxygen
Oxidation (Respiration)
 More efficient energy-generating process
 Molecular oxygen is the final electron acceptor
 Aerobic process in obligate aerobes and facultative
anaerobes
Metabolic Pathways
 Main one is Embden-Meyerhoff
 Convert glucose to pyruvic acid, a key intermediate
 Generates energy in the form of ATP
Metabolic Pathways
 From pyruvic acid:
 Alcoholic fermentation (ethanol) (ex: yeast)
 Homolactic acid fermentation (lactic acid) )ex: strep)
 Heterolactic acid fermentation (lactic acid, CO2, alcohols,
formic and acetic acids
 Propionic acid
 Mixed acid fermentation (lactic, acetic, succinic, and formic)
(ex: e-coli and salmonells)
 Butanediol fermentation: (ex: Kleb, enterobacter & serratia)
 Butyric acid fermentation: (ex: obligate anaerobe)
Metabolic Pathways
 Main oxidative pathway is the Krebs Cycle, resulting in
acid and CO2
 Carbohydrate Utilization & Lactose Fermentation
 “Sugars” = carbohydrates
 Lactose fermentation – key component in identification
schemes
 Lactose is converted to glucose, so ALL lactose
fermenters also ferment glucose
Genetic Elements and Alterations
 Plasmid
 Extra piece of DNA
 Code for antibiotic resistance and other virulence
factors are often found on plasmids
 Sometimes passed from one bacterial species to
another. This is how resistance is acquired.
Plasmid Replication
Genetic Elements and Alterations
 Mutations
 “They don’t always read the book”
 Changes that occur in the DNA code
 Results in changes in the coded protein or in the
prevention of its synthesis
References
 http://media.photobucket.com/image/micro/lovite
x2000/Micro%20biology%20lab/b1cf.jpg?o=81
 http://nhscience.lonestar.edu/biol/wellmeyer/bact
eria/capsules3.jpg
 http://www.iccb.state.il.us/pt3/images/sci/mod11/
bacillus_subtilis.jpg