Fermentation metabolites from Lactobacillus gasseri and Propionibacterium freudenreichii exert bacteriocidal effects in mice.

Lactobacillus gasseri OLL 2716 promotes the elimination of Helicobacter pylori and is utilized in yogurts that are specifically labeled as health foods. On the other hand, milk whey fermented by Propionibacterium freudenreichii ET-3, which increases the numbers of Bifidobacterium, is effective for intestinal disorders. We previously demonstrated that oral administration of L. gasseri and P. freudenreichii fermentation metabolites (LP-FM) improved calf intestinal microflora and reduced the incidence of diarrhea. However, the detailed immunological mechanisms responsible for these effects remain to be fully understood. In this study, we investigated whether LP-FM stimulates the innate immune response and promotes the elimination of Listeria monocytogenes in mice. The C57BL/6 female mice that were treated with LP-FM or L. gasseri fermentation metabolites alone for 4 weeks had more peripheral white blood cells than the untreated control mice. In particular, LP-FM-treated mice had higher CD4- and CD8-positive T-cell counts. The levels of reactive oxygen and nitrogen species produced by peritoneal macrophages were also higher in LP-FM-treated mice. Furthermore, LP-FM-treated mice that were infected with L. monocytogenes exhibited significant enhancement of the elimination of Listeria from the spleen and the liver in comparison with untreated control mice infected with Listeria. The activation of innate immunity by LP-FM was increased by the combination of fermentation metabolites from P. freudenreichii. These results suggest that LP-FM, which contains metabolites from L. gasseri and P. freudenreichii, stimulates the function of the innate immune system, thereby significantly promoting the elimination of L. monocytogenes in mice.