Which of the following organism causes a life-threatening gastroenteritis as a result of use of a broad spectrum antimicrobial agents

The use of broad spectrum antibiotics such as ampicillin and clindamycin has been associated with pseudomembranous colitis. Antibiotic administration results in the proliferation of drug resistant C. difficile that produces Toxin A (a potent enterotoxin with cytotoxic activity) and Toxin B (a potent cytotoxin). This disease is best treated by discontinuing the use of the offending antibiotic and administering oral doses of metronidazole or vancomycin. Administration of antibiotics may also lead to a milder form of diarrhea, called antibiotic associated diarrhea. This form is associated with C. difficile in about 25 percent of the time.