Bile salt toxicity to some bifidobacteria strains: Role of conjugated bilesalt hydrolase and pH

The purpose of this work was to study some aspects of bile salt toxicity to wards bifidobacteria. A strain (Bifidobacterium coryneforme ATCC 25911) was selected for its lack of conjugated bile salt hydrolase activity (CBSH-), and was used with three deconjugating strains (CBSH+), for study of their g rowth and viability in the presence of two dihydroxylated conjugated bile s alts (tauro- and glyco-deoxycholic acids). The presence of the glycoconjuga te induced a more significant growth inhibition for the four strains than t he tauroconjugate. The viability of the strains was measured at several pH levels. Glycodeoxycholic acid, but not taurodeoxycholic acid, exerted a let hal effect, which increased at low pH. This phenomenon was more pronounced for the CBSH- strain. We explain some of these results using an hypothesis based on the consequence of dissociation of conjugated and deconjugated bil e salts, and the value of their pK(a).