Colitis. Endoscope view of an inflamed and nodular colon (large intestine) caused by pseudomembranous colitis (PMC). This is due to a toxin released by an over-abundance of Clostridium difficile bacteria. Plaques (yellow) of mucus and dead cells build up on the walls. Symptoms include diarrhoea and abdominal pain. C. difficile bacteria are normally present in the intestines of some people, but only proliferate when a course of antibiotics removes the other bacteria with which they compete. PMC is treated with cessation of the causative course of antibiotics and the use of other drugs to kill the Clostridium bacteria.