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. Which of the following is the most likely organism causing acute cholangitis? 
Select and explain. 
A. Bacillus fragilis, B. Escherichia coli, C. Streptococcus viridans, D. Pseudomonas aeuroginosa
B: Escherichia coli
Answer: B: Escherichia coli 
Explanation: The most common organisms implicated in acute cholangitis are Escherichia coli (27%), Klebsiella species (16%), Enterobacter, Streptococcus viridans (8%), Enterococcus and anaerobes. Ref: CURRENT Diagnosis and Treatment: Gastroenterology, Hepatology and Endoscopy, 2nd Edition, Chapter 32.