Survival of Probiotic Lactobacilli in Acidic Environments Is Enhanced in the Presence of Metabolizable Sugars

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 10⁶-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.