Exotoxins

Question 1

Exotoxins that inactivate elongation factor (EF-2) via ribosylation, thus inhibiting host cell protein synthesis

Answer 1

• Diptheria toxin (Cornyebacterium diptheriae) - pharyngitis with pseudomembranes and severe LAD (bull neck)
• Exotoxin A (Pseudomonas) - host cell death

Question 2

Exotoxins that inactivate 60S ribosome by removing adenine from rRNA, thus inhibiting host cell protein synthesis

Answer 2

• Shiga toxin (Shigella) - dysentery (via GI mucosal invasion) and HUS (via cytokine release)
• Shiga-like toxin (EHEC) - HUS (via cytokine release); EHEC does not invade host cells

Question 3

Exotoxins that overactivate adenylate cyclase by ribosylation, increasing cAMP, and thus increasing fluid secretion

Answer 3

• Heat-labile toxin (ETEC) - watery diarrhea (“labile in the air, stable on the ground”)
• Cholera toxin (Vibrio cholera) - voluminous “rice-water” diarrhea; toxin permanently activates G_s

Question 4

Exotoxin that mimics the adenylate cyclase enzyme, increasing cAMP, and thus increasing fluid secretion

Answer 4

• Edema factor (Bacillus anthracis) - likely responsible for characteristic edematous borders of black eschar in cutaneous anthrax (lethal factor causes necrosis)

Question 5

Exotoxin that overactivates guanylate cyclase, increasing cGMP, and thus increasing fluid secretion

Answer 5

• Heat-stable toxin (ETEC) - watery diarrhea (“labile in the air, stable on the ground”)

Question 6

Exotoxin that overactivates adenylate cyclase (increasing cAMP) by disabling G_i, thus impairing phagocytosis of the microbe

Answer 6

• Pertussis toxin (Bordetella pertussis) - “whooping cough”

Question 7

Exotoxins (proteases) that cleave SNARE proteins required for neurotransmitter release

Answer 7

• Tetanospasmin (Clostriudium tetani) - toxin prevents release of GABA and glycine (inhibitory NTs) from Renshaw cells in spinal cord, leading to spasticity, risus sardonicus, and “lockjaw”
• Botulinum toxin (Clostridium botulinum) - toxin prevents release of ACh (stimulatory) signals at NMJ, leading to flaccid paralysis and floppy baby

Question 8

Exotoxins that lyse cell membranes

Answer 8

• Alpha toxin (Clostridium perfringens) - phospholipase (lecithinase) that degrades tissue and cell membranes; results in myonecrosis (“gas gangrene”) and hemolysis (“double zone” of hemolysis on blood agar)
• Streptolysin O (Strepococcus pyogenes) - lyses RBC cell membranes, contributing to beta-hemolysis

Question 9

Superantigens that cause shock via induced release of INF-gamma and IL-1

Answer 9

• Toxic shock syndrome toxin (S. aureus) - fever, rash, shock; other S. aureus toxins cause scalded skin syndrome and food poisoning (enterotoxin)
• Exotoxin (Streptococcus pyogenes) - toxic shock syndrome

Question 10

Exotoxin that induces actin depolymerization leadin to mucosal cell death

Answer 10

• Cytotoxin B (Clostridium difficile) - necrosis of colonic mucosal surfaces and pseudomembrane formation