Determination of bile acid conversion potencies of intestinal bacteria by screening in vitro and subsequent establishment in germfree rats.

More than 100 facultatively and strictly anaerobic strains from 22 genera isolated from the digestive tract of the rat were tested for the ability to split glycine and taurine conjugates and to transform cholic acid. Strains belonging to 14 of these genera, of which 12 were strictly anaerobic, were capable of splitting conjugates; whereas strains from only 7 genera were capable of transforming cholic acid. None of the strains isolated could 7a-dehydroxylate cholic acid. Twenty strains from 9 genera capable of splitting conjugates in vitro were established as monocontaminats in ex-germfree rats. Of these, three strains from the genera Clostridium, Eubacterium and Streptococcus (strictly anaerobic species) gave approximately 80 per cent splitting of the caecal bile acids. Four strains showed no conversion of caecal bile acids, while the remainder showed splitting varying between 4 and 44 per cent of the caecal bile acids. Therie was no correlation between the viable numbers of bacteria in the caecum and the extent of splitting of caecal bile acids. Deconjugation in vitro cannot be used as a criterion for the potential deconjugation of microorganisms growing in the digestive tract.