Background: Male circumcision (MC) reduces the risk of HIV. Foreskin inflammation induced by specific genital bacteria could elicit local immune responses, promoting inflammation and recruitment of HIV target cells. MC decreases genital anaerobes; however, direct associations between penile microbiota and inflammatory markers have not been demonstrated. We assessed the penile microbiota and cytokine levels in 138 uncircumcised men from Rakai, Uganda.
Methods: Microbiota were characterized using DNA extracted from a coronal sulcus swab eluent by 16S rRNA gene-based qPCR and V3V4 pyrosequencing, obtaining a total of 371,653 sequences. Genital bacteria present at >0.05% of total sequences were included in the analysis. Using the total microbiota density measured by qPCR and microbiota proportional abundance from sequencing, we calculated the microbiota absolute abundance. Eluent levels of 14 cytokines were measured using an electrochemiluminescent detection platform, and correlated with the absolute abundance of genital bacteria using a quasi-Poisson regression model. Model comparisons were performed by chi-square test.
Results: Only IL-8 levels were sufficient to permit quantitative correlation (Median = 0.72 log10, IQR = 0.18-1.38 log10). Among penile bacteria significantly reduced by MC in prior studies, 11 were positively correlated with IL-8 levels in univariate analyses, including Prevotella, Porphyromonas, Finegoldia, Peptoniphilus, Peptostreptococcus, Anaerococcus, Dialister, Mobiluncus, Actinomyces, Sutterella, and Unclassified Clostridiales Family XI. In multivariate analysis Prevotella (Δ= +49.6% in IL-8 per 10-fold increase in Prevotella spp, P=0.048) and Peptostreptococcus (Δ= +34.0%, in IL-8 per 10-fold increase, P<0.001) abundances were associated with increased IL-8 levels, with a similar trend for Staphylococcus (Δ= +21.5%, P=0.062). In contrast Corynebacterium, which are increased post-MC, were associated with lower IL-8 levels (Δ= -22.8%, P=0.0058).
Conclusions: Prevotella and Peptostreptococcus, which are decreased by MC, were associated with significant increases in penile IL-8, while Corynebacterium, which increases post-MC, was associated with lower IL-8. These findings suggest that post-MC changes in microbiota may reduce inflammatory cytokines and HIV susceptibility.