Caecal Bile Acid Compositions in Gnotobiotic Mice Associated with Human Intestinal Bacteria with the Ability to Transform Bile Acidsin vitro

Abstract

Germfree mice were orally inoculated with human intestinal bacteria for which the ability to transform bile acids was confirmed by in 6itro screening. Three weeks after inoculation, their caecal bile acids were examined. Free-form bile acids were detected in the caecal contents of gnotobiotic mice associated with deconjugating bacteria, Clostridium ramosum R-18 (above 10%) or extremely oxygen sensitive Clostridium M-7 (3.6%). Deoxycholic acid was observed only in the caecal contents of gnotobiotic mice associated with a combination of deconjugating and 7a-dehydroxylating bacteria, i. e. strain R-18 and Eubacterium lentum-like c-25 (4.3%) or a combination of strain R-18 and unidentified Gram-positive rod strain HD-17 (1.1%). 7-Oxo-deoxycholic acid was detected in the caecal contents of gnotobiotic mice associated with strain M-7 (7a-dehydrogenating in 6itro) (1.3%) or strain R-18 plus strain M-7 (2.4%). These results suggest that caecal bile acid composition in gnotobiotic mice reflected the results of bacterial activity in 6itro, but bacterial transforming ability itself is insufficient for normal bile acid transformation comparable to that of conventional mice.