Clostridium difficile colitis or pseudomembranous colitis is colitis (inflammation of the large intestine) resulting from infection with Clostridium difficile, a spore-forming bacterium.It causes an infectious diarrhea called C. difficile associated diarrhea (CDAD).lostridium difficile is one such type of bacterium. In addition to proliferating in the bowel, C. difficile also produces toxins. Without either toxin A or toxin B, C. difficile may colonize the gut, but is unlikely to cause pseudomembranous colitis.