Review: Bacterial transformations of bile acids

The microbial transformation of bile acids that takes place in the lower alimentary tract plays an important role in the in vivo metabolism of bile acids and also of cholesterol in general. Most of the transforming reactions involved can be reproduced in in vitro cultures of mixed intestinal microflora: hydrolysis of the peptide bond in the conjugated bile acids, removal of the 7 alpha-OH group, and dehydrogenation of the alpha-OH substituents at C-7, C-3 and C-12. The last reaction, which leads to the formation an oxo group, is reversible and a stereospecific reduction of, the oxo moiety into a b-OH group has been shown to be carried out.