This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
[{'content': 'Most common organism responsible for, pseudomembranous colitis is: \nSelect and explain. \nA. Clostridium difficile, B. Clostridium botulism, C. Clostridium histolyticum, D. Clostridium butyricum', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Clostridium difficile(Ref: Harrison, 19th/e, p. 1091, 1092 and 17th/e, p. 819, 820; Ananthanarayan, 9th/e, p. 265 and 8th/e, p. 263)* Pseudomembranous colitis is the advanced form of Clostridium difficile-associated disease (CDAD).* Pseudomembranous colitis is diagnosed by detection of one or both C difficile toxins in stool and by endoscopic observation of pseudo membranes or micro abscesses in patients who have diarrhea and have been given antibiotics.", 'role': 'assistant'}]