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: Anatomy
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 viridans, D. Pseudomonas aeruginosa
A: Escherichia coli
Answer: A: Escherichia coli 
Explanation: Cholangitis Ascending bacterial infection of the biliary ductal system with obstruction MC cause of acute cholangitis is choledocholithiasis MC organisms present in the bile in patients with cholangitis : E.coli, Klebsiella pneumoniae, streptococcus faecalis & Bacteroides fragilis Ref:Sabiston 20th edition Pgno :1507