Opacity Proteins Increase Neisseria gonorrhoeae Fitness in the Female Genital Tract Due to a Factor under Ovarian Control

The neisserial opacity (Opa) proteins are a family of antigenically distinct outer membrane proteins that undergo phase-variable expression. Opa+variants of Neisseria gonorrhoeae strain FA1090 are selected in a cyclical pattern from the lower genital tract of estradiol-treated mice. Here we show that cyclical recovery of Opa+gonococci does not occur in ovariectomized mice; therefore, the reproductive cycle plays a role in the selection kinetics in vivo. As predicted by the selection pattern shown by wild-type gonococci, we demonstrated that a constitutive Opa-expressing strain was more fit than an Opa-deficient mutant in the early and late phases of infection. We found no evidence that Opa-mediated colonization selects for Opa+variants during murine infection based on adherence assays with cultured murine epithelial cells. We also tested the hypothesis that complement selects for Opa protein expression during infection. Although some Opa+variants of a serum-sensitive derivative of strain FA1090 were more resistant to the bactericidal activity of normal human serum, selection for Opa expression was not abrogated in C3-depleted mice. Finally, as previously reported, Opa+gonococci were more sensitive to serine proteases. Thus, proteases or protease inhibitors may contribute to the observed in vivo selection pattern. We concluded that Opa proteins promote persistence of N. gonorrhoeae in the female genital tract and that opa gene phase variation allows gonococci to evade or capitalize upon unidentified host factors of the mammalian reproductive cycle. This work revealed an intimate interaction between pathogen and host and provides evidence that hormonally related factors shape bacterial adaptation.