BackgroundProbiotics, especially in combination with non-digestible oligosaccharides, may balance the gut microflora while multistrain preparations may express an improved functionality over single strain cultures. In vitro gastrointestinal models enable to test survival and growth dynamics of mixed strain probiotics in a controlled, replicable manner.MethodsThe robustness and compatibility of multistrain probiotics composed of bifidobacteria and lactobacilli combined with mixed prebiotics (galacto-, fructo- and xylo-oligosaccharides or galactooligosaccharides and soluble starch) were studied using a dynamic gastrointestinal tract simulator (GITS). The exposure to acid and bile of the upper gastrointestinal tract was followed by dilution with a continuous decrease of the dilution rate (de-celerostat) to simulate the descending nutrient availability of the large intestine. The bacterial numbers and metabolic products were analyzed and the growth parameters determined.ResultsThe most acid- and bile-resistant strains were Lactobacillus plantarum F44 and L. paracasei F8. Bifidobacterium breve 46 had the highest specific growth rate and, although sensitive to bile exposure, recovered during the dilution phase in most experiments. B. breve 46, L. plantarum F44, and L. paracasei F8 were selected as the most promising strains for further studies.ConclusionsDe-celerostat cultivation can be applied to study the mixed bacterial cultures under defined conditions of decreasing nutrient availability to select a compatible set of strains.

The effect of stress pretreatment on survival of probiotic Lactobacillus acidophilus La-5, Lactobacillus rhamnosus GG, and Lactobacillus fermentum ME-3 cultures was investigated in the single bioreactor gastrointestinal tract simulator (GITS). The cultures were pregrown in pH-auxostat, subjected to temperature, acid, or bile stress treatment, fast frozen in liquid nitrogen (LN(2)), and tested for survival in GITS. After LN(2) freezing the colony forming ability of L. rhamnosus GG and L. fermentum ME-3 nonstressed and stressed cells was well retained (average survival of 75.4 +/- 18.3% and 88.0 +/- 7.2%, respectively). L. acidophilus La-5 strain showed good survival of auxostat nonstressed cells after fast freezing (94.2 +/- 15.0), however the survival of stress pretreated cells was considerably lower (30.8 +/- 8.5%). All LN(2) frozen auxostat cultures survived well in the acid phase of the GIT simulation (survival 81 +/- 21%); however, after the bile phase, the colony formation ability of L. acidophilus La-5, L. rhamnosus GG, and L. fermentum ME-3 decreased by approximately 1.4 +/- 0.2, 3.8 +/- 0.3, and 3.5 +/- 1.2 logarithmic units, respectively. No statistically relevant positive effect of stress pretreatments on survival of LN(2) frozen L. acidophilus La-5, L. rhamnosus GG, and L. fermentum ME-3 in GITS was observed.

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