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
Most common organism, responsible for pseudomembranous colitis is: 
Select and explain. 
A. Clostridium difficile, B. Clostridium botulism, C. Clostridium bifermentans, D. Clostridium histolyticum
A: Clostridium difficile
Answer: A: Clostridium difficile 
Explanation: Pseudomembranous colitis refers to swelling or inflammation of the large intestine (colon) due to an overgrowth of Clostridium difficile (C. difficile) bacteria. 
This infection is a common cause of diarrhea after antibiotic use.