A 60-year-old diabetic develops rapidly spreading crepitant wound infection of the lower limb with foul-smelling discharge. X-ray shows gas in soft tissues. Anaerobic culture grows large, box-car shaped Gram-positive rods with subterminal spores that are non-swelling. Double zone of haemolysis is seen on blood agar. Which organism is this?
- A Clostridium perfringens ✓
- B Clostridium tetani
- C Clostridium novyi
- D Clostridium septicum
Explanation
Clostridium perfringens is the classic cause of gas gangrene (clostridial myonecrosis). It produces box-car shaped, large Gram-positive rods with subterminal spores that do NOT swell the cell (unlike C. tetani with terminal drumstick spores). The characteristic double zone of haemolysis on blood agar — inner zone of complete haemolysis by theta-toxin and outer zone of incomplete haemolysis by alpha-toxin (lecithinase C) — is pathognomonic. Nagler's reaction (lecithinase activity inhibited by antitoxin on egg-yolk agar) confirms the species. Treatment: high-dose penicillin G plus surgical debridement.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.