Intrauterine colonization with Gardnerella vaginalis and Mobiluncus mulieris induces maternal inflammation but not preterm birth in a mouse model

Abstract

Problem: Preterm birth (PTB) remains a leading cause of childhood mortality. Recent studies demonstrate that the risk of spontaneous PTB (sPTB) is increased in individuals with Lactobacillus-deficient vaginal microbial communities. One proposed mechanism is that vaginal microbes ascend through the cervix, colonize the uterus, and activate inflammatory pathways leading to sPTB. This study assessed whether intrauterine colonization with either Gardnerella vaginalis and Mobiluncus mulieris alone is sufficient to induce maternal-fetal inflammation and induce sPTB.

Method of study: C56/B6J mice, on embryonic day 15, received intrauterine inoculation of saline or 10⁸ colony-forming units of G. vaginalis (n = 30), M. mulieris (n = 17), or Lactobacillus crispatus (n = 16). Dams were either monitored for maternal morbidity and sPTB or sacrificed 6 h post-infusion for analysis of bacterial growth and cytokine/chemokine expression in maternal and fetal tissues.

Results: Six hours following intrauterine inoculation with G. vaginalis, M. mulieris, or L. crispatus, live bacteria were observed in both blood and amniotic fluid, and a potent immune response was identified in the uterus and maternal serum. In contrast, only a limited immune response was identified in the amniotic fluid and the fetus after intrauterine inoculation. High bacterial load (10⁸ CFU/animal) of G. vaginalis was associated with maternal morbidity and mortality but not sPTB. Intrauterine infusion with L. crispatus or M. mulieris at 10⁸ CFU/animal did not induce sPTB, alter pup viability, litter size, or maternal mortality.

Conclusions: Despite inducing an immune response, intrauterine infusion of live G. vaginalis or M. mulieris is not sufficient to induce sPTB in our mouse model. These results suggest that ascension of common vaginal microbes into the uterine cavity alone is not causative for sPTB.

Keywords: intrauterine infection; intrauterine inflammation; mouse model; preterm birth; vaginal microbiome.