Transformation of Bile Acids by Members of the Enterobacteriaceae

Abstract

Eighty-nine strains of microorganisms belonging to the family Enterobacteriaceae were examined for ability to deconjugate taurocholic acid (TCA) and to metabolize cholic acid (CA) and chenodeoxycholic acid (CDCA). They were grown in the presence of each bile acid in several kinds of modified peptone-yeast extract broth. After aerobic or anaerobic incubation for a definite period of time, the culture fluids were collected and analyzed quantitatively for bile acid composition by gas-liquid chromatography.
The 89 strains consisted of 15 strains of Escherichia coli, 12 of Shigella, 56 of Salmonella, and 6 of miscellaneous species. None of them were able to split TCA. Fourteen E. coli strains and two Shigella strains were active in causing 7α-dehydrogenation of CA and CDCA as the sole reaction involved. Both acids were metabolized at a more or less similar rate. A variety in the composition of basal medium caused little change in the rate and extent of transformation. The reaction occurred to a considerable degree in anaerobic cultures, though enhanced in aerobic cultures. A reversible conversion was evidenced between CDCA and its oxidation product, 7-ketolithocholic acid (7KL). The reductive conversion of 7KL into CDCA proceeded to a far less extent than the oxidative process of CDCA into 7KL. No epimerizing reduction of 7KL to ursodeoxycholic acid (UDCA) was observed. No strains were capable of decomposing UDCA. The 7α-dehydrogenation took place in the CDCA moiety in its conjugates without deconjugation.