Degradation of bile salts by human intestinal bacteria.

It is now well established that some component of the intestinal flora is capable of degrading bile salts, since the rate of turnover of 14C-cholic acid in germfree rats has been shown to be only one fifth of that in normal rats (Gustafsson, Bergstrbm, Lindstedt, and Norman, 1957). Further, caecal fluid and faecal suspensions degrade cholic acid, producing a variety of products, including deoxycholic acid and a number of keto acids (Norman and Bergman, 1960; Hamilton, 1963; Norman and Shorb, 1962; Portman, Shah, Antonis, and Jorgensen, 1962; Danielsson, Eneroth, Hellstrbm, and Sjovall, 1962; Norman and Widstrom, 1964). The bile acids as secreted into the intestine are conjugated with taurine or glycine, but those isolated from the faeces are largely unconjugated (Danielsson, Eneroth, Hellstrom, Lindstedt, and Sjovall, 1963; Norman and Palmer, 1964). Although the deconjugation has generally been attributed to the bacteria of the intestine, attempts to isolate in pure culture the organisms able to perform this hydrolytic reaction (or any other step in the degradation of bile) have been largely unsuccessful. Clostridia and enterococci have been shown to deconjugate bile (Norman and Grubb, 1955) and Escherichia coli and C. perfringens can produce a keto acid from cholate (Norman and Bergman, 1960) but these organisms are minor components of the intestinal flora (Drasar and Shiner, 1967, in preparation), and it seems unlikely that they could account for all of the deconjugation and degradation that occurs. In a preliminary communication (Drasar, Hill, and Shiner (1966) reported that Bacteroides spp. were able to deconjugate bile salts (Fig. la). In this paper we report an extension of that study. We have now tested a much greater number of strains of bacteria and a wider range of species for their ability to deconjugate bile salts (the first step in bile degradation) and also for their ability to carry out a further step in the degradation, the removal of the 7-hydroxyl group from free cholic acid (Fig. lb).