This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
[{'content': 'A patient of post-cholecystectomy biliary stricture has undergone an ERCP three days ago. Following this she has developed acute cholangitis. The most likely organism is \nSelect and explain. \nA. Escherichia colli, B. Bacillus fragilis, C. Streptococcus viridans, D. Pseudomonas aerogenosa', 'role': 'user'}, {'content': "Answer: A \nExplanation: The most common bacteria linked to ascending /acute cholangitis is Escherichia coli(25-50%),followed by other gram negative bacilli like Klebsiella(15-20%),proteus and pseudomonas.Among gram positive,enterococcus is common(10-20%)and anaerobes like Clostridium. Reference:SRB's manual of surgery,5th edition,page no:643", 'role': 'assistant'}]