Anaerobes in the genital microbiome have been associated with HIV acquisition in both men and women. Prevotella bivia and Dialister micraerophilus are associated with HIV risk and genital inflammation in both men and women despite major differences in vaginal and penile microbiome composition. Little is known regarding the potential transmission of HIV-associated anaerobes, particularly the directionality of transmission.
We characterized sub-preputial microbiota in uncircumcised HIV negative males, including non-sexually active adolescents (aged 15-17 yrs, N=95) and sexually active adult men (mean age 22 yrs, N=47) in Rakai, Uganda. Sub-preputial swabs were collected into 1% BSA in PBS with protease inhibitor. Total bacterial density was measured by qPCR and proportional and absolute abundance of penile bacteria was characterized by sequencing of the 16S rRNA V3V6 region. Overall penile microbiome composition was compared by PerMANOVA test. Prevalence and abundance of penile bacteria were compared by Chi-square test and Wilcoxon rank-sum test, respectively.
Penile microbiome composition differed significantly between sexually active and non-sexually active uncircumcised males in both proportion and absolute abundances (PerMANOVA p<0.001 in both). However, the total bacterial density was similar in both groups. Non-sexually active adolescents had high abundances of anaerobic penile bacteria, including many Prevotella and Dialister species; however, the two species associated with HIV risk and inflammation—P. bivia and D. micraerophilus—were significantly less prevalent and abundant in non-sexually active adolescents, in contrast to sexually active men (Chi2 and Wilcoxon p<0.05 for both organisms). Peptostreptococcus anaerobius, associated with HIV risk in men, was also less prevalent and abundant in non-sexually active adolescents (Chi2 and Wilcoxon p<0.05). Other anaerobes—including Porphyromonas and Murdochiella—were more abundant in non-sexually active adolescents than sexually-active men.
Prior to initiation of sexual activity, the uncircumcised penile microbiome is dominated by anaerobic bacteria, but the specific species associated with HIV risk and genital inflammation are conspicuously rare. These data suggest that seroconversion-associated anaerobes may originate in the vaginal microbiome, which once when transmitted to penile microbiome could spur foreskin inflammation and colonize the penile microbiome.