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 rhamnos us, Lactobacillus acidophilus, Lactobacillus gasseri, Bifidobacterium adolescentis, Bifidobacterium bifidum, Bifidobacterium breve, Bifidoba cterium infantis, Bifidobacterium longum, Lactococcus lactis spp. lact is, and Streptococcus salivarius spp. thermophilus were tested for the ir ability to produce deoxycholic acid from cholic acid. The productio n of deoxycholic acid was quantitatively measured by radiochromatograp hic analysis in anaerobically prepared washed whole resting cells and by HPLC analysis in growing cultures. Resting whole cells from a posit ive 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-deoxych olic acid, when the cell suspension was incubated anaerobically at a c oncentration 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 cho lic acid under the same conditions. In growing cultures, 91.5% of 150 mu g/ml of cholic acid was transformed to deoxycholic acid and 1.1% to 7-ketodeoxycholic acid by E. lentum-like c-25 after a 7-d anaerobic i ncubation. None of the test strains showed production of either deoxyc holic acid or 7-ketodeoxycholic acid as growing cultures.