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

Background/Aims: 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 7α-dehydroxylation in the intestines. The levels and activities of bile acid 7α-dehydroxylating bacteria have been reported to be increased in gallstone patients. The aim of the current study was to isolate 7α-dehydroxylating bacteria from gallstone patients and determine if these individuals are colonized by similar bacterial species. Methods: The levels of 7α-dehydroxylating bacteria in fecal samples were determined by fecal dilutions in 24 gallstone patients and 10 controls. 7α-Dehydroxylating bacteria were isolated by a non- selective streak plate technique and 7α-dehydroxylation activity was determined by measuring the conversion of [14C]-cholic acid to [14C]-deoxycholic acid using thinlayer chromatography. Results: Gallstone patients had >42-fold (p<0.01) higher levels of 7α-dehydroxylating bacteria than patients who had not developed gallstones. Eighteen strains of 7α-dehydroxylating bacteria were isolated from eight gallstone patients. Attempts to isolate 7α-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. Conclusion: Gallstone patients have higher levels of 7α-dehydroxylating fecal bacteria and appear to harbor only members of the genus Clostridium with this activity.