Following acute pharyngitis, a patient was on broad spectrum antibiotics. One week later he developed watery diarrhoea with a foul odour and abdominal cramps. Antibiotic induced colitis is confirmed. What is the most common cause of antibiotic induced colitis?

Clostridium difficile is the major known cause of nosocomial antibiotic-associated diarrhea and colitis. The organism elaborates at least four toxins, including toxin A (an enterotoxin) and toxin B (a cytotoxin). Symptoms and signs include diarrhea, which is usually watery, occasionally bloody, and has a characteristic foul odor; abdominal cramps; vomiting; fever; and leukocytosis. Demonstration of C difficile cytotoxin in the stool is sensitive and specific. Ref: Chang G.J., Shelton A.A., Welton M.L. (2010). Chapter 30. Large Intestine. In G.M. Dohey (Ed), CURRENT Diagnosis & Treatment: Surgery, 13e.