Clostridium difficile–associated diarrhea is caused by two main toxins. Toxin B (cytotoxin) differs from Toxin A (enterotoxin) in its primary mechanism of action in that Toxin B:
- A Activates adenylyl cyclase in enterocytes to increase cAMP
- B Cleaves SNARE proteins to prevent vesicle fusion
- C Glucosylates and inactivates Rho-GTPases, disrupting actin cytoskeleton with 1000-fold greater potency than Toxin A ✓
- D Is a zinc-dependent metalloprotease that cleaves occludin in tight junctions
Correct answer: C. Glucosylates and inactivates Rho-GTPases, disrupting actin cytoskeleton with 1000-fold greater potency than Toxin A
Explanation
Both C. difficile toxins A and B are glucosyltransferases that mono-glucosylate (inactivate) Rho-family GTPases (Rho, Rac, Cdc42), disrupting the actin cytoskeleton, causing cell rounding, loss of tight junction integrity, and apoptosis. Toxin B is approximately 1000× more cytotoxic than Toxin A and is the primary virulence determinant; newer evidence shows Toxin B alone can cause CDI. SNARE cleavage is the mechanism of botulinum/tetanus toxins.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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