Bifidobacterium animalis strain DN-173 010 hydrolyses bile salts in the gastrointestinal tract of pigs

Background: Bile salt hydrolase (BSH) activity is widespread among ingested bifidobacteria and lactobacilli. It is sometimes considered to be beneficial because of its putative lowering effect on cholesterol absorption and sometimes considered to be deleterious because it may compromise normal fat absorption and even promote the formation of secondary cytotoxic bile acids by the resident intestinal flora. However, the true hydrolysis of bile salts in vivo by ingested living bacteria remains unexplored. The aim of the study was to examine whether or not Bifidobacterium animalis DN-173 010 ( used in fermented milks), which demonstrates a BSH activity in vitro, was also active in vivo during its transit in the intestine of pigs. Methods: Direct measurement of total and unconjugated bile acids reabsorbed into the portal vein was done, before and after the pigs had been treated for 2 weeks with two daily doses of approximate to 3.5 . 10(11) colony-forming units of living (6 pigs) or inactivated B. animalis (6 pigs). Results: None of the treatments modified the portal serum concentration of total bile acids over a 6-h postprandial period. Unconjugated bile acids represented up to 44% and 53% of total bile acids after 1 and 2 weeks of treatment with living bacteria, respectively, compared with only 25% ( P < 0.05) before treatment or after 1 or 2 weeks of treatment with inactivated bacteria. Conclusions: Living B. animalis DN-173 010 exhibited a BSH activity in the gastrointestinal tract of pigs, most probably in the small bowel. There was no sign of increased formation of secondary bile acids beyond the hydrolysis reaction.