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Periodontitis caused by gingival infection is as a risk factor for preterm birth. The periodontal pathogen Fusobacterium nucleatum has been associated with sPTB, PPROM, and stillbirth. F. nucelatum can disrupt gap junctions facilitating membrane disruption and bacterial invasion in vitro. Recently, our metagenomic characterization of the placental microbiome revealed it to (1) resemble the oral microbiome, and (2) vary with sPTB. We thus hypothesized that largely commensal oral bacteria may spread hematogenously to render risk of PTB. We therefore aimed to determine if (1) we could recover live bacteria from the placenta, or (2) the pups after oral inoculation of germ-free (GF) gnotobiotic mice.
We inoculated pregnant GF gnotobiotic mice orally with F. nucleatum and lactobacillus reuteri on day e16.5. A subset received an oral rinse regimen of the hapten TNBS prior to inoculation to induce periodontitis (Fig A). Aseptically dissected placentas and pups were recovered at day 19.5. GF mice or intravenous inoculated mice were used as controls (N=8 mice, 40 placentas and pups). Placentas were assessed by bacterial culture, genotyped, and by fluorescence in situ hybridization (FISH) using probes generic to conserved regions of the 16S gene or L. reuteri specific probes.
For orally inoculated animals, L. reuteri was recovered in 20% of placentas. When periodontitis was induced prior to inoculation, this increased to 50% (p=0.02). Comparatively, intravenously injected animals were also positive for L. reuteri at a 50% rate (Fig B). For the pups, L. reuteri was recovered in 20% of inoculated animals, however, there was no difference between treatment groups. No difference was observed based on placental position in the uterine horn. FISH probes generic to bacterial 16S detected bacteria in 4 of the 5 orally inoculated mice, L. reuteri specific probes identified bacteria in 2 of 5, but not in GF (p=0.14) (Fig C).
The data demonstrates that live and colonizing bacteria can spread hematogenously to the placenta from the oral cavity and that periodontal disease facilitates this migration. These bacteria (in some instances) spread to the pups. These findings have wide implications to perinatal health given the associations of intraamniotic bacteria with sPTB and stillbirth.