Absence of cholic acid 7 alpha-dehydroxylase activity in the strains of Lactobacillus and Bifidobacterium.

To investigate the presence of 7 alpha-dehydroxylase activity on bile acids in the bacterial strains of fermented milk products, 46 strains of Lactobacillus casei, Lactobacillus paracasei, Lactobacillus rhamnosus, Lactobacillus acidophilus, Lactobacillus gasseri, Bifidobacterium adolescentis, Bifidobacterium bifidum, Bifidobacterium breve, Bifidobacterium infantis, Bifidobacterium longum, Lactococcus lactis spp. lactis, and Streptococcus salivarius spp. thermophilus were tested for their ability to produce deoxycholic acid from cholic acid. The production of deoxycholic acid was quantitatively measured by radiochromatographic analysis in anaerobically prepared washed whole resting cells and by HPLC analysis in growing cultures. Resting whole cells from a positive control strain, Eubacterium lentum-like strain c-25, converted 81.7% of .2 mM cholic acid to deoxycholic acid and 3.7% to 7-keto-deoxycholic acid, when the cell suspension was incubated anaerobically at a concentration of 2 mg of protein/ml for 4 h at pH 7.3. However, none of the test strains investigated in this study was able to transform cholic acid under the same conditions. In growing cultures, 91.5% of 150 micrograms/ml of cholic acid was transformed to deoxycholic acid and 1.1% to 7-keto-deoxycholic acid by E. lentum-like c-25 after a 7-d anaerobic incubation. None of the test strains showed production of either deoxycholic acid or 7-keto-deoxycholic acid as growing cultures.