Survival of probiotic lactobacilli in acidic environments is enhanced in the presence of metabolizable sugars

Abstract

Lactobacillus rhamnosus GG is an industrially significant probiotic strain with proven health benefits. In this study, the effect of glucose on L. rhamnosus GG survival was analyzed in simulated gastric juice at pH 2.0. It was found that the presence of 19.4 mM glucose resulted in up to 6-log10-enhanced survival following 90 min of exposure. Further work with dilute HCl confirmed that glucose was the sole component responsible. Comparative analysis with other Lactobacillus strains revealed that enhanced survival was apparent in all strains, but at different pH values. The presence of glucose at concentrations from 1 to 19.4 mM enhanced L. rhamnosus GG survival from 6.4 to 8 log10 CFU ml(-1) in simulated gastric juice. The mechanisms behind the protective effect of glucose were investigated. Addition of N',N'-dicyclohexylcarbodiimide to simulated gastric juice caused survival to collapse, which was indicative of a prominent role in inhibition of F0F1-ATPase. Further work with neomycin-resistant mutants that exhibited 38% to 48% of the F0F1-ATPase activity of the parent confirmed this, as the survival in the presence of glucose of these mutants decreased 3 x 10(6)-fold compared with the survival of the wild type (which had a viability of 8.02 log10 CFU ml(-1)). L. rhamnosus GG survival in acidic conditions occurred only in the presence of sugars that it could metabolize efficiently. To confirm the involvement of glycolysis in the glucose effect, iodoacetic acid was used to inhibit glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity. The reduction in GAPDH activity caused survival to decrease by 8.30 log10 CFU ml(-1) in the presence of glucose. The data indicate that glucose provides ATP to F0F1-ATPase via glycolysis, enabling proton exclusion and thereby enhancing survival during gastric transit.

FIG. 1.

Survival of L. rhamnosus GG (•), L. gasseri ATCC 33323 (□), L. salivarius UCC 500 (▵), L. rhamnosus E800 (♦), and L. paracasei NFBC 338 (▪) in simulated gastric juice, pH 2.0. The data are the means of triplicate experiments, and the error bars indicate standard deviations.

FIG. 2.

(a) Survival of L. rhamnosus GG in simulated gastric juice containing glucose, pH 2.0 (▪), and dilute HCl, pH 2.0 (▴); (b) survival of L. rhamnosus GG in simulated gastric juice, pH 2.0, without lysozyme (▴), KCl (•), glucose (♦), CaCl₂ (▪), pepsin (▵), or KH₂PO₄ (○); (c) survival of L. rhamnosus GG in dilute HCl, pH 2.0, in the presence (▴) or absence (▪) of 19.4 mM glucose. The data are the means of triplicate experiments, and the error bars indicate standard deviations.

FIG. 3.

(a) Survival of stationary-phase L. rhamnosus GG in simulated gastric juice, pH 2.0, containing glucose (▪), glucose and DCCD (□), no glucose (♦), or no glucose and DCCD (▴). (b) Survival of stationary-phase parent (w/t) and neomycin-resistant L. rhamnosus GG (m5, m8, m14, and m18) cultures in simulated gastric juice containing glucose, pH 2.0, following 45 min of exposure (bars) and ATPase activity of permeabilized cells (▵). The data are the means of triplicate experiments, and the error bars indicate standard deviations.

FIG. 4.

Survival of stationary-phase L. rhamnosus GG cultures in simulated gastric juice, pH 2.0, containing glucose (▪), glucose and IAA (▾), no glucose (▴), or no glucose and IAA (♦).