A wound infection in a diabetic patient progresses to crepitant myonecrosis. Gram stain shows large Gram-positive rods. The Nagler reaction on egg-yolk agar (inhibited by specific antitoxin) is positive. The major virulence toxin is:

• A Tetanospasmin
• B Botulinum neurotoxin
• C Enterotoxin
• D Alpha toxin (lecithinase / phospholipase C) ✓

Explanation

Clostridium perfringens alpha toxin, a phospholipase C (lecithinase), is the principal virulence factor in gas gangrene (clostridial myonecrosis). It hydrolyses phosphatidylcholine in cell membranes, causing lysis of red blood cells, platelets, and muscle cells and producing the characteristic opalescence on egg-yolk agar (Nagler reaction), inhibited by specific antitoxin. C. perfringens type A (responsible for gas gangrene) is identified by the Nagler test on Neomycin blood agar. Gas in tissue results from fermentation producing CO2 and H2.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.