Survival and beneficial effects of propionibacteria in the human gut: in vivo and in vitro investigations

Propionibacteria, which are largely used as Swiss-type cheese starters, also constitute promising human probiotics because of their beneficial effects on intestinal bifidobacteria and bacterial enzyme activities. To be efficient, they must survive acid stress imposed within the stomach and the surfactant effects of bile salts. We thus investigated the ability of Propionibacterium freudenreichii (strain Propiofidus(R) SI41) to adapt to, and survive these stresses. In an in vivo study, 7 volunteers received Propiofidus(R) SI41 in 3 different modes. The probiotic was supplied during 3 periods (i) in classical capsules at a low dose (5 x 10(9) CFU.d(-1)), (ii) in the same capsules at a higher dose (5 x 10(10) CFU.d(-1)) (iii) in acid-resistant capsules at the low dose. In the first case, propionibacteria were recovered above 10(5) CFU.g(-1) in only 8 out of 14 faecal samples. In the two following cases, they were enumerated in all faecal samples between 10(5) and 10(7) CFU.g(-1). The recovery of live propionibacteria in faecal samples seemed to be related to a higher content in short chain fatty acids. This study, which clearly showed the role of gastric protection in the survival of propionibacteria, led us to investigate stress adaptation in this strain. Acid tolerance response was evidenced: transient exposure to pH 5 afforded protection towards acid challenge at pH 2. Moreover, we showed that pre-exposure to a moderate bile salts pre-treatment at 0.2 g.L-1 sharply increased its survival against a subsequent lethal challenge (1 g.L-1). Important changes in cellular protein synthesis were observed during adaptation using two-dimensional electrophoresis. Global protein synthesis decreased during adaptation treatments. In contrast, specific proteins were overexpressed during acid adaptation and others during bile salts adaptation. Among the up-regulated polypeptides, a carboxyl carrier protein (BCCP) and the recombinase RecR were identified during both stress responses while the universal chaperonins GroEL and GroES, as well as the replicase RepB, were only up-regulated during acid adaptation. These results bring new insights on the tolerance of P. freudenreichii to acid and bile salts, which should be taken into consideration for the development of probiotic preparations.