Vaginal microbial dynamics and pathogen colonization in a humanized microbiota mouse model

Abstract

ABSTRACTVaginal microbiota composition is associated with differential risk of urogenital infection. Although vaginalLactobacillusspp. are thought to confer protection through acidification, bacteriocin production, and immunomodulation, lack of anin vivomodel system that closely resembles the human vaginal microbiota remains a prominent barrier to mechanistic discovery. We performed 16S rRNA amplicon sequencing of wildtype C57BL/6J mice, commonly used to study pathogen colonization, and found that the vaginal microbiome composition varies highly both within and between colonies from three distinct vivaria. Because of the strong influence of environmental exposure on vaginal microbiome composition, we assessed whether a humanized microbiota mouse (HMbmice) would model a more human-like vaginal microbiota. Similar to humans and conventional mice,HMbmice vaginal microbiota clustered into five community state types (hmCST). Uniquely,HMbmice vaginal communities were frequently dominated by Lactobacilli orEnterobacteriaceae. Compared to genetically-matched conventional mice,HMbmice were less susceptible to uterine ascension by urogenital pathobionts group BStreptococcus(GBS) andPrevotella bivia, but no differences were observed with uropathogenicE. coli. Specifically, vaginalEnterobacteriaceaeandLactobacilluswere associated with the absence of uterine GBS. Anti-GBS activity ofHMbmice vaginalE. coliandL. murinusisolates, representingEnterobacteriaceaeandLactobacillusrespectively, were characterizedin vitroandin vivo. AlthoughL. murinusreduced GBS growthin vitro, vaginal pre-inoculation withHMbmouse-derivedE. coli, but notL. murinus, conferred protection against vaginal GBS burden. Overall, theHMbmice are an improved model to elucidate the role of endogenous microbes in conferring protection against urogenital pathogens.IMPORTANCEAn altered vaginal microbiota, typically with little to no levels ofLactobacillus, is associated with increased susceptibility to urogenital infections, although mechanisms driving this vulnerability are not fully understood. Despite known inhibitory properties ofLactobacillusagainst urogenital pathogens, clinical studies withLactobacillusprobiotics have shown mixed success. In this study, we characterize the impact of the vaginal microbiota on urogenital pathogen colonization using a humanized microbiota mouse model that more closely mimics the human vaginal microbiota. We found several vaginal bacterial taxa that correlated with reduced pathogen levels but showed discordant effects in pathogen inhibition betweenin vitroandin vivoassays. We propose that this humanized microbiota mouse platform is an improved model to describe the role of the vaginal microbiota in protection against urogenital pathogens. Furthermore, this model will be useful in testing efficacy of new probiotic strategies in the complex vaginal environment.