Which of the following species of clostridium causes pseudomembranous colitis?

Pseudomembranous colitis is diagnosed by detection of one or both Clostridium difficile toxins in stool and by endoscopic observation of pseudomembranes or microabscesses in patients who have diarrhea and have been given antibiotics. Plaques and microabscesses may be localized to one area of the bowel. The diarrhea may be watery or bloody, and the patient frequently has associated abdominal cramps, leukocytosis, and fever. Most common antibiotics associated with pseudomembranous colitis are, Ampicillin Clindamycin Fluoroquinolones (recently) The disease is treated by discontinuing administration of the offending antibiotic and orally giving either metronidazole or vancomycin. Also know: Administration of antibiotics results in proliferation of drug-resistant C difficile that produces two toxins. Toxin A, a potent enterotoxin that also has some cytotoxic activity, binds to the brush border membranes of the gut at receptor sites. Toxin B is a potent cytotoxin. Ref: Brooks G.F. (2013). Chapter 11. Spore-Forming Gram-Positive Bacilli: Bacillus and Clostridium Species. In G.F. Brooks (Ed), Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e.