A 55-year-old diabetic male presents with rapidly spreading necrosis of the scrotal and perineal skin with crepitus. Blood cultures grow a Gram-positive, spore-forming, anaerobic bacillus that produces a lecithinase (alpha toxin) demonstrating a positive Nagler reaction. Which organism is MOST likely responsible?
- A Clostridium tetani
- B Clostridium perfringens ✓
- C Bacteroides fragilis
- D Clostridium botulinum
Correct answer: B. Clostridium perfringens
Explanation
Clostridium perfringens is the classic cause of gas gangrene and Fournier's gangrene; its major virulence factor is alpha toxin (a lecithinase/phospholipase C) which produces a positive Nagler reaction on egg-yolk agar (opacity neutralised by specific antitoxin). C. tetani produces tetanospasmin and shows terminal spores (drumstick), C. botulinum produces botulinum toxin, and B. fragilis is a non-spore-forming anaerobe that does not produce lecithinase.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.