Clostridium difficile is a type of bacteria that is the most common cause of severe infections involving the colon. It is normally seen after antibiotic use, which kills the normal gut bacteria. Symptoms include frequent, watery, or foul smelling stool. It is diagnosed by examining the stool for the bacterium. Taking a course of antibiotics to kill the clostridium bacteria is the recommended treatment. The prognosis is good once the infection has been treated.