An anaerobic, spore-forming, Grampositive bacillus; it can colonize the intestinal tract, where overgrowth (superinfection) commonly occurs after ingestion of oral antibiotics; this organism produces two toxins—an enterotoxin that causes antibiotic associated diarrhea (AAD) and a cytotoxin that causes pseudomembranous colitis (PMC); a common cause of healthcare-associated infections