Intestinal microflora and bile acids. In vitro cholic acid transformation by mixed fecal culture of rats.

In vitro cholic acid (CA) transformation by mixed fecal culture was investigated. Concentrations of glucose, peptone, and yeast extract in the medium and the initial pH of the medium markedly affected the CA transformation. Yeast extract enhanced the transformation, whereas high concentrations of glucose and peptone inhibited it. When the initial pH of the medium was below 6.5, CA was converted to 7-keto-deoxycholic acid (7KD), and formation of deoxycholic acid (DC) was not observed. In contrast, with an initial pH of 7.0, about 60% of the CA was converted to 7KD after 3 days of incubation, and then DC gradually formed after 4 days of incubation, following the disappearance of 7KD. The formation of DC in the cultured samples was paralleled in each case by disappearance of 7KD. In pure culture systems, Escherichia coli and some strains of Bacteroides formed 7KD from CA. No DC formation was observed in pure cultures of any of the strains examined.