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
Most common cause of cholangitis - 
Select and explain. 
A. Viral infection, B. CBD stone, C. Surgery, D. Amoebic infection
B: CBD stone
Answer: B: CBD stone 
Explanation: Gall stones are the most common cause of obstruction in cholangitis.

Other causes are

benign & malignant strictures
parasites
instrumentation of the ducts and indwelling stents
partially obstructed biliary enteric anastomosis

Most common organisms cultured from bile in patients with cholongitis include

Escherichia coli
Klebsiella pneumoniae
Streptococcus faecalis
Enterobacter
Bacteroides fragilis