Cervical epithelial damage promotes Ureaplasma parvum ascending infection, intrauterine inflammation and preterm birth induction in mice

Around 40% of preterm births are attributed to ascending intrauterine infection, and Ureaplasma parvum (UP) is commonly isolated in these cases. Here we present a mouse model of ascending UP infection that resembles human disease, using vaginal inoculation combined with mild cervical injury induced by a common spermicide (Nonoxynol-9, as a surrogate for any mechanism of cervical epithelial damage). We measure bacterial load in a non-invasive manner using a luciferase-expressing UP strain, and post-mortem by qPCR and bacterial titration. Cervical exposure to Nonoxynol-9, 24 h pre-inoculation, facilitates intrauterine UP infection, upregulates pro-inflammatory cytokines, and increases preterm birth rates from 13 to 28%. Our results highlight the crucial role of the cervical epithelium as a barrier against ascending infection. In addition, we expect the mouse model will facilitate further research on the potential links between UP infection and preterm birth.


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For the damage assessment (Figures 1-3), a pilot study was conducted to determine sample size as there were no available data from previous studies. Data from the pilot study showed such a remarkable effect that a decision was made not sacrifice more mice, in line with the 3 R's. For the rest of data (Figures 4-9), the power calculation was based on our primary outcome, which was preterm birth induction. Our main hypothesis was that the combination treatment of N9+UP would result in higher PTB rates compared to treatment with vehicle controls. A small pilot study was conducted to estimate projected PTB rate in the N9+UP group (25%). PTB rate for vehicle group was estimated from previously published studies (0%). An allocation ration of 1.5 was decided to factor in potential adverse outcomes in the treatment group as the combination of N9 and UP has never been tested on mice before. To compare the proportions, a Fisher's exact test would be performed. Power was pre-specified at 80% and a error at 0.05.
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