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BACTERIA
An Overview
Staphlococcus aureus
and human white
blood cells
Bacteria are
single-celled,
microscopic,
prokaryotic organisms
that we rely on and fight on a daily basis
“On any possible, reasonable or fair
criterion, bacteria are—and always
have been—the dominant forms of life
on Earth.” – Stephen Jay Gould, 1996
Basic Characteristics:
Prokaryotic- no true nucleus, no membrane-bound organelles – different from
eukaryotes (which make up all multi-cellular organisms and lots of single-celled
organisms, too)
Single-celled organisms
Cell walls contain a peptidoglycan – aka murien – a polymer of sugars and acids
found only in bacteria that forms a meshlike layer protecting the cell membrane
Tiny - measured in units called micrometers (μm - 1 micrometer = 0.0001 cm)
Lack a true nucleus; instead, have a region called the ‘nucleoid region‘where DNA
congregates
DNA is free floating (no membrane surrounding DNA)
May have additional DNA which is not associated with this nucleoid region (called a
plasmid)
Other Characteristics:
Rapid growth and cell division (binary fission) under favorable conditions
Mutants that arise from bacteria can become extremely resilient organisms
because bacteria can:
Grow and reproduce cells quickly
Adapt quickly to changing environments
Plasmids impart additional resistant characteristics to bacteria via
cell-to-cell transfer of this extra DNA material
Capable of colonizing in almost any environment
The overall form of a basic bacterial cell is that of a complex cell envelope
that encloses cell cytoplasm. Cell appendages from the envelope protrude
into the environment surrounding the cell.
Parts of a bacterial cell:
Pili: hair-like appendages used for pulling
bacteria along surfaces or to exchange genetic
information (plasmids) – sex pili
Fimbriae: filamentous protein outgrowths from
cell envelope used to adhere to one another and
to other cells
Capsule:
Attachment to surfaces; protection
against phagocytic engulfment, occasionally killing
or digestion; reserve of nutrients or protection
against desiccation
Cell wall:
found on all bacteria – can be thick
or thin – thick = Gram +ve, thin = Gram –ve due to
response to Gram stain
Outer membrane and Plasma
membrane : Permeability barrier; transport
of nutrients and wastes; energy generation;
location of numerous enzyme systems - outer
membrane in Gram –ve species only
Cytoplasm: aqueous solution that bathes and
surrounds everything inside the cell
Nucleoid region: DNA gathers here
Plasmids: DNA that can be copied and passed to
other bacteria without going through reproduction
Ribosomes: Protein synthesis
Flagellum: long, whip-like appendage used for
locomotion
Bacteria are one of the three domains – we further classify
bacteria into phyla, class, order, family, genus, species as
best we can, based on many different characteristics. We will
cover the basic characteristics useful in classifying pathogenic
bacteria.
Classifying Bacteria
Most microbiologists classify bacteria according to a phylogenetic classification system
based on Bergey's Manual of Systematic Bacteriology (Bergey's Manual). The Bergey's
Manual is a guide to distinguishing bacterial species based on phenotypic differences.
For our purpose, and for simplicity's sake, we will use a more basic classification
approach.
We can classify bacteria according to:
Shape
Cell wall structure and the Gram Stain
Cellular respiration
Public Health and Doctors also use Growth Media as an indicator
A couple of other criteria for classification:
Forming endospores
Mycolic acids
SHAPE
3 general shapes:
Cocci: spherical shape
Bacillus: rod shape
Spirochetes: spiral shape
GRAM STAINS
CAPSULES
USE OF OXYGEN
(RESPIRATION)
PUTTING IT ALL TOGETHER CLASSIFYING
Domain: Bacteria
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gamma Proteobacteria
Order: Enterobacteriales
Family: Enterobacteriaceae
Genus: Escherichia
Species: Escherichia coli (E. coli)
E. coli in intestine of a human
SEROTYPES
Try to match the following by using your new
classification skills: