Clostridium difficile produces two major toxins in hospital-associated diarrhoea. Toxin B (cytotoxin) differs from Toxin A (enterotoxin) in which property relevant to clinical diagnostics?
- A Toxin B is approximately 10-fold more potent as a cytotoxin and is present even in Toxin A-negative strains causing disease ✓
- B Toxin B is detectable by ELISA while Toxin A is only detected by cell cytotoxicity assay
- C Toxin A disrupts actin cytoskeleton; Toxin B causes fluid secretion only
- D Toxin B is encoded by the tcdB gene on a chromosomal island separate from the PaLoc
Explanation
Toxin B (TcdB) is approximately 1,000-fold more cytotoxic than Toxin A (TcdA) in cell culture assays, due to its glucosyltransferase activity targeting Rho GTPases causing cytoskeletal collapse. Clinically important: some C. difficile strains produce Toxin B only (Toxin A-negative/Toxin B-positive variant), which still causes disease. This means testing only for Toxin A by EIA (old-generation tests) would miss these infections. Current guidelines recommend GDH antigen + Toxin A&B EIA, or GDH + PCR for tcdB, or nucleic acid amplification testing as the preferred diagnostic strategy. Both toxins are encoded within the pathogenicity locus (PaLoc).
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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