Isolated fecal microorganisms capable of 7-alpha-dehydroxylating bile acids.

Strains of microorganisms capable of 7alpha-dehydroxylation of chenodeoxycholate were isolated from rat and human feces. All the strains were strictly anaerobic, non-motile, moderately themioresistant Gram-positive rods. They showed some saccharolytic properties with the production of both acid and gas. They were H(2)S-positive but indole-, skatole-, citrate-, catalase-, and oxidase-negative. The isolated strains capable of 7alpha-dehydroxylation of chenodeoxycholate were also able to oxidize the hydroxyl groups at C-3 and C-7 to keto groups. The following metabolites were isolated: 3-keto-7alpha-hydroxy-5beta-cholanoic acid, 3alpha-hydroxy-7-keto-5beta-cholanoic acid, 3alpha-hydroxy-5beta-cholanoic acid, and 3-keto-5beta-cholanoic acid. The isolated strains did not have the enzymes necessary for hydrolyzing conjugated bile acids. In mixed anaerobic cultures of fecal microorganisms, extensive reduction of the 3-keto group to the 3beta-hydroxyl group occurred. The microorganism(s) responsible for this reaction have as yet not been isolated.