Transformation of bile acids and sterols by clostridia (fusiform bacteria)in Wistar rats

The effects on bile acid and sterol transformation of clostridia (fusiform bacteria), the dominant intestinal bacteria in rodents (ca. 10(10) counts p er g wet feces) were examined in Wistar rats. After inoculation of clostrid ia into germ-free rats and into rats previously inoculated solely with Esch erichia coil, most of the endogenous bile acids were deconjugated, and chol ic acid and chenodeoxycholic acid were 7 alpha-dehydroxylated to deoxycholi c acid and lithocholic acid, respectively. Tauro-beta-muricholic acid, anot her major bile acid in rats, was deconjugated, but only part of it (ca. 30% ) was transformed into hyodeoxycholic acid. Cholesterol and sitosterol were also reduced to coprostanol and sitostanol, respectively. Escherichia coil transformed neither bile acids nor sterols. These data suggest that clostr idia play an important role in the formation of secondary bile acids and co prostanol in rats.