Caracterisation moleculaire de bacteriophages de bacteries lactiques

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Isolates from normal human intestinal flora but not lactic acid bacteria exhibit 7α- and 7β-hydroxysteroid dehydrogenase activities

Ursodeoxycholic acid (UDCA)-producing bacteria are of clinical and industrial interest due to the multiple beneficial effects of this bile acid on human health. UDCA is the 7 b -OH epimer of the primary (i.e. synthesized by the liver) bile acid chenodeoxycholic acid (CDCA). Epimerization proceeds in two subsequent and reversible steps, catalysed by a 7 a - and a 7 b -hydroxysteroid dehydrogenase (7 a - and 7 b - HSDH), with 7oxo-lithocholic acid (7oxo-LCA) as the intermediate product. The aim of this study was to test the 7 a - and 7 b -HSDH activities of anaerobic whole cell cultures of a number of lactic acid bacteria and human intestinal isolates, using CDCA, UDCA and 7oxo- LCA as the substrates. Among 140 strains tested, 21 exhibited at least one of both 7-HSDH activities. 7 a -HSDH activity was detected in six strains, 7 b -HSDH in nine strains, and both activities in six other strains. All active strains were isolated from normal human and infant faeces. They belonged to the genera Clostridium , Eubacterium and Ruminococcus , whereas no strain of Lactobacillus , Bifidobacterium or Streptococcus was found to be active under our study conditions. The present study therefore revealed, for the first time, a number of normal human intestinal isolates supporting the epimerization of CDCA to UDCA, and further extended our knowledge of those intestinal bacteria which are responsible for 7 a -or7 b -HSDH activity. Key words: screening, bile acids, epimerization, intestinal microflora, lactic acid bacteria, probiotics

Increasing ursodeoxycholic acid in the enterohepatic circulation of pigs through the administration of living bacteria

International audienceWe investigated the feasibility of increasing ursodeoxycholic acid (UDCA) in the enterohepatic circulation of pigs by administering living bacteria capable of epimerising endogenous amidated chenodeoxycholic acid (CDCA) to UDCA. We first demonstrated that combining Bifidobacterium animalis DN-173 010, as a bile salt-hydrolysing bacterium, and Clostridium absonum ATCC 27555, as a CDCA to UDCA epimerising bacterium, led to the efficient epimerisation of glyco- and tauro-CDCA in vitro, with respective UDCA yields of 55·8 (se 2·8) and 36·6 (se 1·5)%. This strain combination was then administered to hypercholesterolaemic pigs over a 3-week period, as two daily preprandial doses of either viable (six experimental pigs) or heat-inactivated bacteria (six controls). The main effects of treatment were on unconjugated bile acids (P=0·035) and UDCA (P<0·0001) absorbed into the portal vein, which increased 1·6–1·7- and 3·5–7·5-fold, respectively, under administration of living compared with inactivated bacteria. In bile, UDCA did not increase significantly, but the increase in biliary lithocholic acid with time in the controls was not observed in the experimental pigs (P=0·007), and the same trend was observed in faeces. All other variables (biliary lipid equilibrium, plasma lipid levels and partition of cholesterol between the different lipoprotein classes) remained unaffected by treatment throughout the duration of the experiment. In conclusion, it is feasible to increase the bioavailability of UDCA to the intestine and the liver by administering active bacteria. This may represent an interesting new probiotic activity, provided that in future it could be expressed by a safe food micro-organis