Selection for expression of the gonococcal hemoglobin receptor during menses.

All gonococci encode a hemoglobin (Hgb) receptor, but it is phase variable, and most laboratory and clinical isolates are in the Hgb receptor "off" phase. In the present study, we address the question of whether there is a selective advantage to expressing the Hgb receptor during early phases of the menstrual cycle, when Hgb is readily available from menstrual blood. Inclinical isolates collected from women, Hgb use in vitro (Hgb receptor "on" phase) was associated with a shorter time since the onset of the last menstrual cycle, (P=.031, Wilcoxon rank-sum test). Thus, there may be a selective advantage to expression of the gonococcal Hgb receptor during infection of women in the early phases of their menstrual cycles.