<prompt> Most common organism responsible for pseudomembranous colitis isClostridium difficileClostridium botulismClostridium histolyticumClostridium butyricum  <response>: Clostridium difficile: long, slender, gram-positive bacilli. Non-hemolytic, saccharolytic and weakly proteolytic. Causes: bloody diarrhea, pseudomembranous colitis, a common cause of nosocomial diarrhea. Pathogenesis: high molecular weight exotoxin A and B Toxin A is a potent enterotoxin, Toxin B is a cytotoxin. Reference: Textbook of Microbiology; Anathanarayan and panikers; 10th edition; Page no: 270 