Role of the penile microbiome in female sex partner risk of bacterial vaginosis and sexually transmitted infections: a narrative review

) or by anaerobic bacteria that are associated with bacterial vaginosis (BV), and is influenced by male circumcision status, female partner vaginal microbiome (VMB), BV status, condom use, and antibiotic use. Penile bacteria that are associated with BV and genital mucosal inflammation are associated with men's risk of HIV and STIs. In the few studies that simultaneously evaluate the penile and vaginal microbiome in sex partners, specific taxa are highly correlated, with evidence for bi-directional transmissibility. BV-associated taxa in the PMB are associated with increased risk of BV and STIs in female sex partners. Emergent trials demonstrate that antimicrobial treatment in men can reduce penile anaerobic bacteria and female sex partner's risk of BV recurrence. However, data are lacking on factors influencing penile-vaginal bacterial exchangeability, the durability of bacterial exchange, and the conditions under which exchange may lead to increased risk of adverse outcomes in the index or partner. Optimal and non-optimal PMB have not been defined. Assessment of PMB composition and function across the life course is needed. Association of PMB with intrinsic host factors (genetics and endogenous hormones) is lacking; association with behavioral and lifestyle factors is limited. Addressing these gaps may lead to the development of assays to facilitate screening and monitoring after therapeutic interventions in men and female partners, or the development of therapeutics for optimizing PMB. Studies are needed to refine and develop new treatment and counseling guidelines for men and their sexual partners.