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Microbiology BASIC Bacteriology Part 1
USMLE Step 1
Review Notes
Bacteria are single-celled prokaryotic organisms with several structural elements that distinguish
them from eukaryotes
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Gram-negative
organisms contain much thinner peptidoglycan layers, outer membranes, and periplasmic spaces
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Treponema is too thin to be visualized,
so one must use the dark field microscopy or fluorescent antibody staining to see it
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There are some bacteria that live within cells, some because they must
in order to survive (the obligate intracellular organisms), and others which can live with
themselves that they want to but have mechanisms for surviving extracellular lea if they have
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Some organisms contain catalase, an enzyme
that degrades hydrogen peroxide into water and oxygen
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Some bacteria produce unique pigments when grown on agar that
aid in their identification, such as Actinomyces israelii's yellow sulphur granules
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These toxins have two components, an A subunit and a B
subunit
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Other bacteria that produce ADP-ribosylating toxins include heat-labile and heat-stable
enterotoxigenic E
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Cholera and botulinum toxins
function by cleaving SNARE proteins, which are required for the release of neurotransmitters from
the presynaptic terminal, leading to floppy paralysis
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Another exotoxin
produced by Streptococcus pyogenes is a superantigen
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Endotoxins,
such as LPS, are composed of a combination of a polysaccharide chain and a lipid moiety, which is
usually known as lipid A
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Additionally, it can also lead
to the production of nitric oxide, which ultimately results in hypotension and septic shock
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Once the genetic encoding occurs, it can become packaged into viral capsids which
transfer the toxin genes during infection of other bacteria
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4 Microbiology CLINICAL Bacteriology Part 1

USMLE Step 1
Review Notes
The following algorithm for classifying grampositive microorganisms summarizes how to identify
specific bacterial strains based on their unique characteristics
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Each individual bacterium will be discussed in greater
detail as you move along in the chapter

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