DiseasesDB 2820 MedlinePlus 000259 eMedicine med/1942 MeSH D004761 See also: Clostridium difficile Pseudomembranous colitis, a cause of antibiotic-associated diarrhea (AAD), is an inflammation of the colon . It is often, but not always, caused by the bacterium Clostridium difficile . Because of this, the informal name C. difficile colitis is also