Sexual behavior influences the abundance of Prevotellaceae family in men who have sex with men

The Prevotellaceae family is reported to be more abundant in men who have sex with men (MSM) than in men who have sex with women (MSW), but the impact of sexual behaviors on its composition remains unclear. This study aimed to investigate the potential causal direction of sexual behaviors on Prevotellaceae composition in MSM, with a potential link to HIV infection susceptibility. We enrolled 100 HIV-negative MSM in Chongqing, collected fecal samples for 16S rRNA sequencing, and gathered sexual behavior information via questionnaires. After excluding 5 participants due to ineligible fecal DNA detection results, 95 samples were included in the final analysis. Alpha and beta diversities were calculated and compared using the R vegan package; Linear discriminant analysis (LDA) was performed to identify differentially abundant taxa, with LDA score > 2 considered differentially abundant. Two-sample Mendelian randomization (MR) and mediation analyses based on GWAS summary data inferred causal relationships. MSM with sexually transmitted diseases showed higher Prevotellaceae alpha diversity (P = 0.045). Prevotellamassilia was enriched in illicit drug users or those exposed to HIV-positive partners (LDA score > 2). MR confirmed that same-sex intercourse causally increased Prevotellaceae abundance (Beta = 2.642, P = 0.022). We further explore the mediation roles of Prevotellaceae and other gut microbiota in linking sexual behaviors and HIV infection, but only Defluviitaleaceae exhibited significant (mediation proportion = 9.85%). Prevotellaceae dysbiosis is significantly associated with sexual behaviors in MSM and may promote HIV infection, highlighting the potential of microbiota-targeted interventions for HIV prevention.