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
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- 
Select and explain. 
A. Escherichia coli, B. Bacillus fragilis, C. Streptococcus viridians, D. Pseudomonas aeruginosa
A: Escherichia coli
Answer: A: Escherichia coli 
Explanation: None