A patient on clindamycin for an anaerobic infection develops watery diarrhoea on day 10 of therapy. Stool enzyme immunoassay detects both toxin A and toxin B of Clostridioides difficile. What is the mechanism by which toxin B (TcdB) causes colonocyte damage?

• A Activates adenylyl cyclase increasing cAMP causing secretory diarrhoea
• B Cleaves SNARE proteins preventing neurotransmitter release
• C Glucosylates Rho GTPases, disrupting actin cytoskeleton and tight junctions ✓
• D Acts as a superantigen activating T cells non-specifically

Explanation

C. difficile toxins A (enterotoxin) and B (cytotoxin) are glucosyltransferases that glucosylate and inactivate Rho family GTPases (Rho, Rac, Cdc42). This disrupts actin polymerization and the cytoskeleton, causing colonocyte rounding, tight junction breakdown, fluid secretion, and inflammatory pseudomembrane formation. Toxin B is 1000-fold more potent than toxin A. Cholera toxin activates adenylyl cyclase (cAMP mechanism). Clostridium botulinum toxin cleaves SNARE proteins.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.