A 45-year-old construction worker suffers a penetrating wound of the left leg, which is cleaned and sutured. Three days later, the patient presents with sudden onset of severe pain at the site of injury. Physical examination shows darkening of the surrounding skin, hemorrhage, and cutaneous necrosis. The wound shows a thick serosanguinous discharge with gas bubbles and a fragrant odor. Which of the following is the most likely etiology of this patient's wound infection?

Gas gangrene (clostridial myonecrosis) is a necrotizing, gas-forming infection that begins in contaminated wounds and spreads rapidly to adjacent tissues. The disease can be fatal within hours of onset. Gas gangrene follows the deposition of C. perfringens into tissues under anaerobic conditions. Such conditions occur in areas of extensive necrosis (e.g., severe trauma, war-time injuries, and septic abortions). Clostridial myonecrosis is rare when the wound is subjected to prompt and thorough debridement of dead tissue. Damage to previously healthy muscle is mediated by a myotoxin. C. botulinum (choice A) secretes a preformed neurotoxin.Diagnosis: Gas gangrene, clostridial myonecrosis