This is a classic case of colonization of the gut by C. difficile following ingestion of acid resistant spores. The C. difficile then produces 2 (some strains 3) toxins that activate the inflammatory cascade and also disrupt the cytoskeleton of colonic epithelial cells. This damage causes an outpouring of fibrin and inflammatory cells that form a pseudomembrane in about 50% of cases. In about half of the cases of C. difficile infection the symptoms are the same but a pseudomembrane does not form. Only about 10-20% of post-antibiotic diarrhea is caused by C. difficile. Diagnosis is made by identification of the toxin but the most sensitive and specific method is culture of that bacteria from the stool.