A 65-year-old man undergoes cardiac bypass surgery and is placed on postoperative, broad-spectrum, antibiotic prophylaxis. Several days later, he develops fever, abdominal pain, and bloody diarrhea. Colonoscopic biopsy demonstrates a thick mucopurulent exudate. Which of the following is the most likely etiology of this patient's gastrointestinal disorder?

C. difficile is the most common cause of diarrhea in patients on antibiotic therapy (e.g., clindamycin or cephalosporins) who are hospitalized for more than 3 days. Necrotizing enterocolitis (pseudomembranous colitis) is a disease that may affect the colon in segments or in its entirety. The mucosa is covered by yellow-green, necrotic exudates (pseudo membranes). Food poisoning and necrotizing enterocolitis are caused by the enterotoxins of C. perfringens (choice C). About 48 hours after the ingestion of contaminated meal, patients present with abdominal pain and distention, vomiting, and passage of bloody stools. C. perfringens is also the most common cause of gas gangrene following wound infection or septic abortion. C. tetani (choice D) produces a potent neurotoxin that causes tetany and generalized muscle spasms. Clostridium botulinum (choice A) produces a neurotoxin that causes paralysis.Diagnosis: Pseudomembranous colitis, Clostridium difficile