The foreskin is a site of heterosexual acquisition of HIV-1 among uncircumcised men. However, some men remain HIV-negative despite repeated, unprotected vaginal intercourse with HIV-positive partners, while others become infected after few exposures. The foreskin microbiome includes a diverse group of anaerobic bacteria that have been linked to HIV acquisition. However, these anaerobes tend to coassociate, making it difficult to determine which species might increase HIV risk and which may be innocent bystanders. Here, we show that 6 specific anaerobic bacterial species, Peptostreptococcus anaerobius, Prevotella bivia, Prevotella disiens, Dialister propionicifaciens, Dialister micraerophilus, and a genetic near neighbor of Dialister succinatiphilus, significantly increased cytokine production, recruited HIV-susceptible CD4+ T cells to the inner foreskin, and were associated with HIV acquisition. This strongly suggests that the penile microbiome increases host susceptibility to HIV and that these species are potential targets for microbiome-based prevention strategies.
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