Bacterial vaginosis (BV) is a microbiome-based disease characterized by a lack of Lactobacillus in the vagina. We have covered this disease with multiple blog posts and encourage any interested readers to search for these blogs to learn more. One outstanding question regarding BV is how sexual intercourse affects the disease. One prevailing thought is that the penis can actually be colonized by BV-associated bacteria, and that through sexual intercourse it can be spread between partners. A new paper published last week in mBio suggests this is true.
The researchers measured the penile microbiomes of 165 uncircumcised, black men from Uganda, as well as diagnosing BV status in their female partners. The BV status was measured by Nugent score, which is a bacterial staining technique that basically measures the amount of anaerobic bacteria in the vagina (non-Lactobacilli). The stain produces a score between 1-7 with 1 being healthiest and 7 being least healthy (mostly anaerobic bacteria). After measuring the penile microbiomes, the scientists were able to be categorize them into 7 different community state types (CST1-7). These community state types varied from 1 to 7 in terms of both overall abundance and composition, with CST1 having the lowest density of bacteria and the lowest diversity while CST7 had the highest density and the highest diversity of bacteria.
The scientists compared the female partner’s BV status with the men’s community state type, and noted that having a CST1-7 on the penile microbiome corresponded with a higher likelihood of the female partner being diagnosed with BV. Two genera of bacteria, Corynebacterium and Staphylococcus, on the penile microbiome were associated with healthy vaginal flora, whereas Dialister, Mobiluncus, Prevotella, and Porphyromonas were associated with BV. Interestingly penises that included Lactobacillus and Gardnerella, genera associated with healthy vaginas and BV vaginas, respectively, were not statistically associated with BV status. Overall, men with CST4-7 were significantly more likely to have a sexual partner with BV, and had more BV associated bacteria colonizing their penises. In addition, men with more than one sexual partner were more likely to have CST4-7, and again, their partners more likely to have BV.
It appears that men’s penises, especially uncircumcised ones, can be vectors for bacterial transmission. This simple fact should make us reconsider BV as an STD, and actually fits in well with another that has shown promiscuity is a risk for BV. It is likely that circumcision and condom would decrease BV transmission rate, as they do other STDs, but until a paper comes out that studies this connection no one can say for sure.