A patient develops profuse rice-water diarrhea after a picnic. Stool anaerobic culture shows heat-resistant spore-forming Gram-positive rods producing lecithinase (Nagler reaction positive) on egg-yolk agar. Toxin testing on Vero cells shows enterotoxin with cytotoxic activity. The organism is most likely:
- A Clostridium difficile
- B Bacillus cereus (diarrheal type)
- C Clostridium septicum
- D Clostridium perfringens type A ✓
Explanation
A positive Nagler reaction (opalescence on egg-yolk agar inhibited by C. perfringens antitoxin) is specific for C. perfringens alpha toxin (lecithinase/phospholipase C). Food-borne illness from C. perfringens type A occurs 8–24 hours after ingestion of contaminated meat; the heat-resistant spores survive cooking and germinate when food cools slowly. C. difficile causes pseudomembranous colitis with Toxin A (enterotoxin) and Toxin B (cytotoxin) but does not produce alpha-toxin or a positive Nagler reaction. B. cereus does not produce lecithinase. C. septicum causes gas gangrene, not food poisoning.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.