Gram-⊕, spore-forming, obligate anaerobic rod.

Produces 2 toxins:- Toxin A, an enterotoxin, binds to the brush border of the gut and alters fluid secretion.- Toxin B, a cytotoxin, causes cytoskeletal disruption via actin depolymerization.Both toxins lead to diarrhea → pseudomembranous colitis.

- Often 2° to antibiotic use, especially clindamycin or ampicillin; associated with PPIs. - Can occur as late as 10 weeks after treatment.

- Diagnosed by PCR or antigen detection (EIA for glutamate dehydrogenase antigen) of one or both toxins in stool.- Abdominal x-ray/CT: detection of toxic megacolon, abscesses, perforation, pseudomembranous colitis.

Treatment: oral vancomycin (1st line), metronidazole- For recurrent cases, consider repeating prior regimen, fidaxomicin (macrocyclic antibiotic that inhibits the sigma subunit of RNA polymerase), or fecal microbiota transplant.Control measures: Gloves and protection gown; mask not necessary. Wash hands with soap because spores are resistant to alcoholic disinfectants.