Screening of bile resistance and bile precipitation in lactic acid bacteria and bifidobacteria

A modification of the ecometric method was developed for a rapid screening of bile resistance in lactic acid bacteria and bifidobacteria. Validation o f the MEM bile assay (modified ecometric method) was performed comparing th e bile resistance index (RIbile) and the bile resistance ratio (R%). Most B ifidobacterium strains assayed were bile sensitive (83.3%), while only 62.1 % of lactobacilli showed that behavior. Some bifidobacterial strains (55.6% ) showed a crystalline precipitate when grown on solid medium supplemented with 0.5% ox bile. The crystalline structures produced by B. pseudolongum C IDCA 531 were isolated and analyzed by optical and scanning electron micros copy, thin-layer chromatography, melting point, and specific cholesterol re actions. Those studies confirmed the presence of cholesterol in these cryst alline structures. On the other hand, none of the lactobacilli and streptoc occi studied had the ability to produce crystalline precipitates.