Reduced Live Organism Recovery and Lack of Hydrosalpinx in Mice Infected with Plasmid-Free Chlamydia muridarum

Abstract

ABSTRACTPlasmid-freeChlamydia trachomatisandChlamydia muridarumfail to induce severe pathology. To evaluate whether the attenuated pathogenicity is due to insufficient infection or inability of the plasmidless chlamydial organisms to trigger pathological responses, we compared plasmid-competent and plasmid-freeC. muridaruminfections in 5 different strains of mice. All 5 strains developed hydrosalpinx following intravaginal inoculation with plasmid-competent, but not inoculation with plasmid-free,C. muridarum. The lack of hydrosalpinx induction by plasmid-freeC. muridarumcorrelated with significantly reduced live organism recovery from the lower genital tract and shortened infection in the upper genital tract. The plasmid-freeC. muridarumorganisms failed to induce hydrosalpinx even when the organisms were directly inoculated into the oviduct via an intrabursal injection, which was accompanied by significantly reduced survival of the plasmidless organisms in the genital tracts. Furthermore, plasmid-competentC. muridarumorganisms after UV inactivation were no longer able to induce hydrosalpinx even when directly delivered into the oviduct at a high dose. Together, these observations suggest that decreased survival of and shortened infection with plasmid-freeC. muridarummay contribute significantly to its attenuated pathogenicity. We conclude that adequate live chlamydial infection in the oviduct may be necessary to induce hydrosalpinx.