Background: Neisseria gonorrhoeae is a human-adapted pathogen with a highly plastic genome. Error-prone genomic replication leads to genetic changes that can alter expression and production of virulence factors, where fitness in different niches selects for adaptive variants. Phase variation, where changes in repetitive sequences can turn genes on or off, exemplifies the capacity of N. gonorrhoeae to adapt rapidly. Leveraging gonococcal adaptation in a natural niche, in this case vaginal colonization, has identified the phase variable methyltransferase ModA, as an important factor during infection.
Aims/Methods: We aimed to identify genes important in gonococcal vaginal colonization by comparing in vitro passaged ‘lab-adapted’ with in vivo passaged ‘host-adapted’ strains. We utilized the clinical isolate WHO P in a CEACAM-humanized mouse model of vaginal colonization. We serially plate-passaged isolates in vitro to create lab-adapted strains. These passaged strains were used to infect mice via the lower genital tract. Mice were vaginally lavaged to monitor colonization and to collect in vivo passaged gonococci for subsequent serial passaging and whole genome sequencing. After three passages in vivo, we identified mutations arising in host-adapted strains using comparative genomics. We aim to identify how these mutations impact gonococcal fitness.
Results: Host-adapted N. gonorrhoeae showed increased duration of colonization compared to lab-adapted strains. We have found multiple genes that are repeatedly and independently mutated, most notably phase variation of modA. modA is turned OFF in lab-adapted WHO P, but turned ON in 60% of host-adapted strains and 100% of those that exhibited extended colonization (>10 days). Competition experiments using strains in which modA has been locked ON or OFF indicate that a mixed inoculum of modA ON and OFF best supports vaginal colonization. Our findings suggest that modA ON has a benefit in maintaining vaginal colonization, with a heterogenous population of gonococci being the most fit during infection.
Conclusions: Using comparative genomics of in vitro versus in vivo passaged strains, we have uncovered phase variation to turn modA ON in vivo, that we hypothesize is contributing to the success of N. gonorrhoeae during vaginal colonization. We aim to further investigate the mechanism of action of ModA during infection.