Comparison among fecal secondary bile acid levels, fecal microbiota and Clostridium scindens cell numbers in Japanese

Bile acid 7alpha-dehydroxylation by intestinal bacteria, which converts cholic acid and chenodeoxycholic acid to deoxycholic acid (DCA) and lithocholic acid (LCA), respectively, is an important function in the human intestine. Clostridium scindens is one of the most important bacterial species for bile acid 7alpha-dehydroxylation because C. scindens has high levels of bile acid 7alpha-dehydroxylating activity. We quantified C. scindens and secondary bile acids, DCA and LCA, in fecal samples from 40 healthy Japanese and investigated their correlation. Moreover, we used terminal restriction fragment length polymorphism (T-RFLP) analysis to investigate the effect of fecal microbiota on secondary bile acid levels. There was no correlation between C. scindens and secondary bile acid in fecal samples. On the other hand, T-RFLP analysis demonstrated that fecal microbiota associated with high levels of DCA were different from those associated with low levels of DCA, and furthermore that fecal microbiota in the elderly (over 72 years) were significantly different from those in younger adults (under 55 years). These results suggest that intestinal microbiota have a stronger effect on DCA level than does the number of C. scindens cells.