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212: Fusobacterium nucleatum colonizes the placenta after oral inoculation in a gnotobiotic mouse model

      Objective

      Periodontitis is associated with an increased risk of PTB, although the causal mechanism is poorly characterized. Our recent metagenomic studies of the placenta revealed that it harbors a unique microbiome most similar to the mouth. Fusobacterium nucleatum, a microbe native to subgingival plaques, is both associated with periodontal disease and PTB. Collectively, this has lead to the hypothesis that the placenta is seeded hematogenously and that this process is selective to and facilitated by species native to the oral cavity. We therefore used a germ-free gnotobiotic mouse model to interrogate this potential mechanism of placental colonization.

      Study Design

      Pregnant germ-free (GF) dams (n=3 per group) were inoculated with a simple microbial community of Lactobacillus reuteri & Fusobacterium nucleatum 4 days (4d) prior to anticipated delivery. Bacteria were delivered by tail vein injection (IV) or oral gavage (Oral). For a subset of dams, the oral cavity was pretreated prior to oral gavage with 2,4,6-Trinitrobenzenesulfonic acid (Oral+TNBS) to promote mucosal inflammation. Maternal and fetal tissues were collected by sterile Cesarean 1d prior to anticipated delivery. Microbial DNA was extracted and subjected to qPCR to quantify cecal and placental colonization.

      Results

      The previously germ free maternal cecum was successfully recolonized for all treatment groups (ANOVA p=0.0001, all vs. GF p<0.05). As anticipated, IV administration of bacteria resulted in placental colonization similar to amounts found in control (SPF) mice (p<0.05). Interestingly, oral gavage also resulted in placental colonization at levels similar to both the IV and SPF group. qPCR with species specific primers revealed that placental colonization by bacteria either by IV or by oral gavage was primarily due to the presence of F. nucleatum (ANOVA p=0.029) but not L. reuteri (a gut commensal).

      Conclusion

      These data show that oral gavage of F. nucleatum to a GF dam results in placental colonization at levels similar to non-germ free mice. We speculate this is due to hematogenous dissemination of bacteria from the oral mucosa, given findings among oral gavage groups. Interestingly, this process appears to be selective for certain bacterial species with the inherent capacity to open up endothelial gap junctions (i.e., F. nucleatum).
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