Chlamydia muridarum plasmid induces mouse oviduct pathology by promoting chlamydial survival and ascending infection and triggering host inflammation.

Background: Infection with plasmid-free Chlamydia trachomatis and Chlamydia muridarum fails to induce severe pathology, however, the mechanisms underlying this phenotype are unclear.

Objectives: To elucidate the mechanisms of chlamydial plasmid-mediated pathology in mouse oviducts.

Materials & Methods: BALB/c mice were intravaginally infected with either plasmid-competent or plasmid-free C. muridarum strains. To compare the survival and ascending infection of these strains, vaginal swabs and genital tract tissues were collected and cultured with HeLa cells to monitor the recovery of live organisms. In addition, Chlamydia strains were intrabursally inoculated into the oviducts of mice to assess pathogenicity. Cytokine levels in the vaginal swabs collected from both the plasmid-competent and plasmid-free C. muridarum-infected mice were detected using Bio-Plex Pro Mouse Cytokine, Chemokine, and Growth Factor Assays.

Results: The plasmid-competent C. muridarum strain induced hydrosalpinx formation in mouse oviducts following intravaginal inoculation, however, this was not the case for the plasmid-free C. muridarum strain. The lack of hydrosalpinges in response to the plasmid-free C. muridarum strain correlated with its significantly reduced ability to survive and disseminate to the upper genital tract. Furthermore, the plasmid-free C. muridarum failed to induce hydrosalpinx formation in mice, even when the strain was intrabursally injected into oviducts. A comparison of the cytokine levels in mouse vaginal secretions showed that the plasmid-free C. muridarum strain induced less IL-15, LIF, MIP-2, IL-1α, IL-1β, TNF-α, and RANTES.

Conclusion: C. muridarum plasmid contributes to oviduct pathology by promoting bacterial survival and ascending infection, and triggering host inflammatory responses.