Isolates from Normal Human Intestinal Flora but not Lactic Acid Bacteria Exhibit 7?- and 7?- Hydroxysteroid Dehydrogenase Activities

Abstract

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 7β-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 7α- and a 7β-hydroxysteroid dehydrogenase (7α- and 7β- HSDH), with 7oxo-lithocholic acid (7oxo-LCA) as the intermediate product. The aim of this study was to test the 7α- and 7β-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. 7α-HSDH activity was detected in six strains, 7β-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 7α- or 7β-HSDH activity. Key words: screening, bile acids, epimerization, intestinal microflora, lactic acid bacteria, probiotics.