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: 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 coli, B. Bacillus fragilis, C. Streptococcus viridians, D. Pseudomonas aeruginosa', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]