The toxin of Clostridium difficile that is primarily responsible for colonic cell damage and pseudomembranous colitis is:

• A Toxin A (enterotoxin) — causes intestinal fluid secretion only
• B Binary toxin (CDT) — the sole virulence factor in all strains
• C Toxin B (cytotoxin) — more potent cytotoxin, primarily responsible for colonic cell death ✓
• D Neurotoxin (similar to tetanus toxin) — inhibits glycine release

Explanation

C. difficile produces two major toxins: Toxin A (TcdA, enterotoxin) and Toxin B (TcdB, cytotoxin). Toxin B is 100–1000-fold more potent and is considered the primary virulence factor — it inactivates Rho GTPases, causing cytoskeletal disruption, tight junction loss, and apoptosis of colonocytes. Some PCR-positive strains produce only Toxin B (A-negative, B-positive) and still cause severe disease. CDT (binary toxin) is an additional toxin found in hypervirulent ribotype 027 strains and enhances adherence. TcdB is the primary target of newer therapeutics including bezlotoxumab (monoclonal antibody).

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.