Background Mycoplasma genitalium (MG) is a newly recognised pathogen associated with acute and persistent reproductive tract infection in men and women. Understanding of the disease mechanisms, persistence and immune avoidance of this organism is hampered by the lack of a suitable animal model.
Methods Female pigtail macaques (Macaca nemestrina) were inoculated cervically with ∼109 genome equivalents (∼108 ccu's) of MG strain G37, then assessed at intervals over 8 weeks for the persistence of MG in lower tract specimens. Fallopian tube biopsies were collected via laparotomy at Weeks 4 and 8. Specimens were assessed for the presence of MG DNA by qPCR and for viable MG by growth in H broth and Vero cell co-cultures. Serum collected at intervals was evaluated by immunoblot and ELISA for reactivity to MG antigens. Finally the variable regions of the immunodominant surface antigens, MgpB and MgpC, were analysed by PCR cloning and sequencing to evaluate sequence variation during infection.
Results Of the five primates inoculated cervically with MG, three were infected throughout the 8 weeks of the study, one maintained infection for 4 weeks and one resisted infection. Recovery of viable MG from lower reproductive tract sites was improved by co-culture in Vero cells followed by qPCR to measure an increase in MG genomes during culture. Growth in H broth, as determined by colour change proved an unreliable indicator of the presence of viable MG in the specimen possibly due to the presence of primate microorganisms that inhibit the growth of MG. No viable MG or MG DNA was detected in upper tract tissues in any of the primates perhaps suggesting that longer infection times or repeated inoculations are needed to achieve ascension in this model. Analysis of mgpB variable regions B and G indicated that after 8 weeks of infection the predominant expressed sequence changed from that of the G37C inoculum to 1 to 5 novel sequences consistent with recombination between the expression site and the MgPars. In contrast, no sequence variation was observed in the inoculum grown in vitro for a similar duration. Antibodies reactive with MG antigens, including the variable regions of MgpB and MgpC, were detected by immunoblot and ELISA in serum and cervical exudates.
Conclusions The cervical inoculation model of pigtail macaques results in long-term infection and can be used to study the persistence of MG, development of antibodies and antigenic variation.
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