<prompt> Most common organism responsible for, pseudomembranous colitis is:Clostridium difficileClostridium botulismClostridium histolyticumClostridium butyricum  <response>: Ans. is a i.e., Clostridium difficileRef: Harrison, 19the, p. 1091, 1092 and 17the, p. 819, 820; Ananthanarayan, 9the, p. 265 and 8the, 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. 