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: Microbiology
A patient was on long term antibiotic therapy for peritonitis. During the course of treatment, he develops mucus diarrhea. Most likely cause of diarrhea is: September 2012 
Select and explain. 
A. Peritonitis, B. Antibiotic associated diarrhea, C. Immunocompromised state, D. Altered bowel habits
B: Antibiotic associated diarrhea
Answer: B: Antibiotic associated diarrhea 
Explanation: Ans. B i.e. Antibiotic associated diarrhea Antibiotic-associated diarrhea (AAD)It results from an imbalance in the colonic microbiota caused by antibiotic therapy.Microbiota alteration changes carbohydrate metabolism with decreased sho-chain fatty acid absorption and an osmotic diarrhea as a result.Another consequence of antibiotic therapy leading to diarrhea is overgrowth of potentially pathogenic organisms such as Clostridium difficile.It is defined as frequent loose and watery stools with no other complications.