Final answer:
The most common cause of acute bacterial cholangitis is the blockage of the biliary tree, usually due to gallstones, which can lead to an infection.
Step-by-step explanation:
The most common cause of acute bacterial cholangitis is an obstruction of the biliary tree, often due to gallstones. When the hepatic or common bile ducts are blocked by gallstones, as shown in Figure 6.7.7, bile cannot be excreted normally, which can result in infection. The presence of gallstones is particularly significant as they can create a favorable environment for bacterial growth and cause a blockage, leading to cholangitis. While other conditions such as primary sclerosing cholangitis, primary biliary cirrhosis, and Budd-Chiari syndrome can affect the liver and bile ducts, they are not typically the direct causes of acute bacterial cholangitis.