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Microbiology · USMLE Step 1

USMLE Microbiology: Virulence Factors and Toxins

Bacterial exotoxins, endotoxin, and other virulence factor mechanisms matched to the organism and disease effect they produce.

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What is the mechanism of action of diphtheria toxin?
ADP-ribosylates elongation factor 2 (EF-2), halting host protein synthesis
Which organism produces diphtheria toxin?
Corynebacterium diphtheriae
What is the mechanism of action of cholera toxin?
ADP-ribosylates Gs protein, locking adenylate cyclase on and raising cAMP, driving Cl- and water secretion
What is the mechanism of action of pertussis toxin?
ADP-ribosylates Gi protein, disabling it and raising cAMP
What is the mechanism of E. coli heat-labile toxin (LT)?
ADP-ribosylates Gs protein, increasing cAMP, the same mechanism as cholera toxin
What is the mechanism of E. coli heat-stable toxin (ST)?
Activates guanylate cyclase, increasing cGMP and decreasing resorption of NaCl and water
What is the mechanism of Pseudomonas aeruginosa exotoxin A?
ADP-ribosylates EF-2, inhibiting protein synthesis
What is the mechanism of Shiga toxin?
Removes an adenine from 28S rRNA, inactivating the 60S ribosomal subunit and halting protein synthesis
Which organism produces Shiga toxin?
Shigella dysenteriae
What is the mechanism of tetanus toxin (tetanospasmin)?
Cleaves SNARE proteins to block release of the inhibitory neurotransmitters GABA and glycine
What clinical effect does tetanus toxin produce?
Spastic paralysis
What is the mechanism of botulinum toxin?
Cleaves SNARE proteins to block release of acetylcholine at the neuromuscular junction
What clinical effect does botulinum toxin produce?
Flaccid paralysis
What are the three components of anthrax toxin?
Protective antigen, edema factor, and lethal factor
What is the mechanism of anthrax edema factor?
Mimics adenylate cyclase, raising cAMP

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