This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
In antibiotic associated colitis, organism involved is - 
Select and explain. 
A. Clostridium difficile, B. Pseudomonas, C. Staphylococcus, D. Enterococcus
A: Clostridium difficile
Answer: A: Clostridium difficile 
Explanation: Ans. is 'a' i.e., Clostridium difficile Antibiotic - associated (or clostridium difficile associated) colitis o It is an example of superinfection. o It is caused by alteration of normal bowel flora, which allows multiplication of clostridium difficle which releases several toxins that damage the mucosa of the bowel and promote excretion of fluid. o It takes the form of an acute, nonspecific colitis, i.e. pseudomembranous colitis. o Almost any antimicrobial may initiate this condition, but the drugs most commonly repoed today are injectable cephalosporins and amoxi/ampicillin -- Laurence 9th/e 212 o Clindamycin, not commonly used in routine practice today, had an even greater propensity. o Metronidazole is the DOC for pseudomembranous colitis and vancomycin is an alternative.