Post-coital dynamics of the penile and cervico-vaginal genital microbiome

BACKGROUND: The vaginal and penile coronal sulcus microbiome influence reproductive health outcomes and susceptibility to multiple sexually transmitted infections including HIV. There is evidence that genital bacteria are shared between heterosexual partners during sex, but the dynamics of this microbiota exchange remain poorly understood. RESULTS: Using microbiome characterization from established heterosexual couples, we found that condomless penile-vaginal sex dramatically altered the coronal sulcus microbiome, with transient dominance by Lactobacillus spp. Conversely, condom-protected penile-vaginal sex did not result in significant shifts in overall composition (p = 0.63). Significant changes were observed in the female partner's genital microbiome, including increased Corynebacterium spp. and increased abundance of Bacteria Associated with Seroconversion, Inflammation, and Cells (BASICs) (Prevotella bivia, Peptostreptococcus anaerobius, Dialister micraerophilus, Prevotella disiens, Dialister propionicifaciens, Dialister succinatiphilus) in individuals with a colonized male partner. By 72 h post-coitus L. iners cell-normalized abundance remained elevated in the penile microbiome, but other taxa returned to baseline levels. Causal mediation analysis indicated a pH-mediated increase in vaginal Gardnerella at 72 h. CONCLUSIONS: Condom-protected penile-vaginal sex was associated with minimal genital microbiome changes, whereas condomless penile-vaginal sex among established couples led to extensive exchange of genital microbiota. Most disruptions to the microbiome resolved within 2-3 days, although changes in vaginal pH were associated with longer-lasting increases in Gardnerella abundance. Video Abstract.