It is believed that obstruction of the common bile duct leads to increased colonization of the duodenum by bacteria and these can reach the common bile duct and then the intrahepatic bile ducts by retrograde infection or be carried by portal venous blood. Note in the images that the infection is primarily seen in the portal triads and the liver seems affected only secondarily. Partial obstruction carries a greater risk of cholangitis than complete obstruction. Klebsiella is the most common bacteria found but Enterobacter, E. coli, enterococci, and Streptococcus are also frequently cultured. More than one bacteria may be cultured from infected ducts or from the blood.