Molecular genetic evidence of bacterial colonization of cholesterol gallstones.

BACKGROUND/AIMS Cholesterol gallstone formation is believed to be unrelated to the presence of bacteria because attempts to culture potentially causative bacteria from surgically removed cholesterol stones have failed. However, the formation of gallbladder gallstones takes years. Embedded bacteria may be damaged or killed. The aim of this study was to search for bacterial DNA sequences in cholesterol stones with negative bacterial culture. METHODS Bacterial gene fragments were amplified in vitro from DNA extracted from cholesterol gallbladder stones. Comparative 16S ribosomal RNA sequence analysis was used for identification. RESULTS Gallstones with cholesterol content between 70% to 90% harbored bacterial DNA (16 of 17 patients). No bacterial DNA was found in the gallstones with cholesterol content of > 90% (3 patients). Three bacterial groups typical for gallstone colonization were identified. Propionibacteria-related DNA was found in the stones of 9 patients (45%). Enterobacterial type sequences were obtained in 5 patients (25%). A more heterogenous sequence collection was retrieved from 7 patients (35%) and could be assigned to the major bacterial line of gram-positive bacteria with a low DNA guanine and cytosine content. CONCLUSIONS Most cholesterol gallstones harbor bacterial DNA. It is important to determine the actual role of these microorganisms in gallstone formation.