Lactobacillus by-products inhibit the growth and virulence of uropathogenic Escherichia coli

Uropathogenic strains of Escherichia coli (UPEC) can colonize the vagina and cause infections within the entire urogenital tract, including those associated with urinary tract devices. Lactobacilli typically dominate the vaginal microbiota in healthy women, and studies have shown that they can inhibit UPEC growth and vaginal colonization. However, little is known regarding the mechanisms behind these effects. Using a luciferase-based reporter construct, gradients of lactic acid, hydrogen peroxide and spent culture supernatants (SCS) from urogenital probiotic strains Lactobacillus rhamnosus GR-1 and L. reuteri RC-14 were examined for their effects on growth and virulence factor expression in UPEC isolate C1212. In a dose- and pH- dependent manner, lactic acid, hydrogen peroxide and Lactobacillus SCS all strongly inhibited UPEC C1212 growth and increased the promoter activity of outer membrane proteins (OMPs) A and X, two porins normally upregulated in response to UPEC membrane stress. Lactic acid and the culture supernatants also downregulated the promoter activity of the major subunits of type 1 and P fimbriae, critical adherence factors within the urogenital tract. Our findings indicate that compounds secreted by lactobacilli likely protect the urogenital tract from UPEC colonization and infection by inhibiting growth, inducing stress and downregulating proteins critical for host attachment.