The 'good' bacteria in your gut often keep bad stuff at bay. When the good guys are destroyed (possibly with antibiotics), C. difficile takes over, which can cause severe diarrhea or deadly inflammation of the colon. The condition most commonly affects hospitalized older adults or those in long-term care. The cure: more antibiotics — or a fecal transplant."
The Human Microbiome: A Rogue's Gallery | KQED QUEST