<i>Lactobacillus crispatus</i> Limits Bladder Uropathogenic <i>E. coli</i> Infection by Triggering a Host Type I Interferon Response

Abstract

Many urinary tract infections (UTIs) are recurrent because uropathogens persist within the bladder epithelial cells (BECs) for extended periods between bouts of infection. Because persistent uropathogens are intracellular, they are often refractive to antibiotic treatment. The recent discovery of endogenous <i>Lactobacillus</i> spp. in the bladders of healthy humans raised the question of whether these endogenous bacteria directly or indirectly impact intracellular bacterial burden in the bladder. Here, we report that in contrast to healthy women, female patients experiencing recurrent UTIs have a bladder population of <i>Lactobacilli</i> that is markedly reduced. Exposing infected human BECs to <i>L. crispatus</i> in vitro markedly reduced the intracellular uropathogenic <i>Escherichia coli</i> (UPEC) load. The adherence of <i>Lactobacilli</i> to BECs was found to result in increased type I interferon (IFN) production, which in turn enhanced the expression of cathepsin D within lysosomes harboring UPECs. This lysosomal cathepsin D-mediated UPEC killing was diminished in germ-free mice and type I IFN receptor-deficient mice. Secreted metabolites of <i>L. crispatus</i> seemed to be responsible for the increased expression of type I IFN in human BECs. Intravesicular administration of <i>Lactobacilli</i> into UPEC-infected murine bladders markedly reduced their intracellular bacterial load suggesting that components of the endogenous microflora can have therapeutic effects against UTIs.