Light micrograph section through human colon tissue showing pseudomembranous colitis. Also known as, antibiotic-associated colitis or C. difficile colitis. This condition refers to inflammation of the colon associated with an overgrowth of the bacterium Clostridiodes difficile (formerly known as Clostridium difficile). Pseudomembranous colitis occurs when certain bacteria, usually C. difficile, rapidly outgrow other bacteria that normally keep natural healthy balance in check. Certain toxins produced by C. difficile, which are usually present in tiny amounts, rise to the levels high enough to damage the colon.