Isolation and characterization of cholic acid 7α-dehydroxylating fecal bacteria from cholesterol gallstone patients

Abstract

The development of cholesterol gallstones, in some patients, has been associated with increased proportions of deoxycholic acid in the bile acid pool. Deoxycholic acid is a microbial product of cholic acid 7alpha-dehydroxylation in the intestines. The levels and activities of bile acid 7alpha-dehydroxylating bacteria have been reported to be increased in gallstone patients. The aim of the current study was to isolate 7alpha-dehydroxylating bacteria from gallstone patients and determine if these individuals are colonized by similar bacterial species. The levels of 7alpha-dehydroxylating bacteria in fecal samples were determined by fecal dilutions in 24 gallstone patients and 10 controls. 7alpha-Dehydroxylating bacteria were isolated by a non-selective streak plate technique and 7alpha-dehydroxylation activity was determined by measuring the conversion of [14C]-cholic acid to [14C]-deoxycholic acid using thin-layer chromatography. Gallstone patients had >42-fold (p<0.01) higher levels of 7alpha-dehydroxylating bacteria than patients who had not developed gallstones. Eighteen strains of 7alpha-dehydroxylating bacteria were isolated from eight gallstone patients. Attempts to isolate 7alpha-dehydroxylating bacteria from ten control patients were unsuccessful using identical isolation techniques. Surprisingly, all strains of bacteria isolated from gallstone patients appear to belong to the genus Clostridium. Gallstone patients have higher levels of 7alpha-dehydroxylating fecal bacteria and appear to harbor only members of the genus Clostridium with this activity.