Isolation and Characterization of Bile Acid 7‐Dehydroxylating Bacteria from Human Feces

Abstract

Methods for isolation of fecal 7α‐dehydroxylating bacteria are presented. A total of 219 strains were isolated from feces of healthy humans, and their ability to 7‐dehydroxylate cholic, chenodeoxycholic, and ursodeoxycholic acids were examined. Of all the isolates, 14 strains were found to be capable of eliminating the hydroxy group at C‐7α and/or C‐7β. All the isolates were strictly anaerobic, Gram‐positive rods. Thirteen isolates were non‐sporeforming bacteria showing certain saccharolytic properties with the production of acid and gas from dextrose, and were catalase‐positive but indole‐, lecithinase‐, urease‐ and oxidase‐negative. Based on the data available at present, it was concluded that they could be regarded as members of the genus Eubacterium. One strain, however was identified as Clostridium sordellii. The isolated strains capable of 7α‐dehydroxylating cholic acid and chenodeoxycholic acid were also able to oxidize the hydroxy group at C‐7α. Nine strains (10, 12, 36S, M‐2, M‐17, M‐18, Y‐98, Y‐1112, and Y‐1113) of the 7α‐dehydroxylating bacteria were confirmed to have 7β‐dehydroxylation ability, but five strains (O‐51, O‐52, O‐71, O‐72, and Y‐67) could not transform ursodeoxycholic acid to lithocholic acid.

Consequences of bile salt biotransformations by intestinal bacteria

“…56,57 Bacteria capable of converting primary to secondary bile acids have been isolated from humans. [58][59][60] The rodent isolate required unidentified Bacteroides spp. in co-culture due to an unidentified syntrophy.…”

Assignment of Eubacterium sp. VPI 12708 and related strains with high bile acid 7alpha-dehydroxylating activity to Clostridium scindens and proposal of Clostridium hylemonae sp. nov., isolated from human faeces.

“…Many studies (Archer et al, 1982 ;Ferrari et al, 1977 ;Hayakawa & Hattori, 1970 ;Hirano et al, 1981 ;Stellwag & Hylemon, 1979 ;Takamine & Imamura, 1995 ;White et al, 1980) on faecal bacteria having 7α-dehydroxylating activity have been reported. In these reports, the multistep bile acid 7α-dehydroxylation pathway was studied in detail only for strain VPI 12708 (Baron et al, 1991 ;Coleman et al, 1987 ;Doerner et al, 1997 ;Franklund et al, 1993 ;Mallonee & Hylemon, 1996 ;Mallonee et al, 1990Mallonee et al, , 1992.…”

“…Members of the genera Clostridium and Eubacterium are the predominant intestinal species exhibiting bile acid 7α-dehydroxylating activity (Archer et al, 1982 ;Ferrari et al, 1977 ;Hayakawa & Hattori, 1970 ;Hirano et al, 1981 ;Stellwag & Hylemon, 1979 ; Takamine & Imamura, 1995). The presence of this activity in the intestinal microflora results in 7α-dehydroxylation of cholic acid and chenodeoxycholic acid, yielding deoxycholic acid and lithocholic acid, respectively.…”

“…However, detailed studies concerning taxonomic research on strain VPI 12708 have not appeared. Takamine & Imamura (1995) isolated and characterized some strains of bile acid 7α-dehydroxylating bacteria and concluded that a few strains were members of the genus Eubacterium. Doerner et al (1997) assessed bile acid 7α-dehydroxylating bacteria for the presence of a bai-like gene by Southern hybridization.…”

PCR Detection Method of Clostridium scindens and C. hiranonis in Human Fecal Samples

“…A number of laboratories have isolated bile acid 7a-dehydroxylating bacteria from fecal samples but it was not easy to isolate them because of their small population (13,14). The level of fecal bacteria capable of bile acid 7a-dehydroxylation in normal humans ranges from 10 2 to 10 5/g of wet weight feces (14).…”