Study suggests penile microbiome can transmit bacterial vaginosis by sexual intercourse

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.

Sex, body mass index, and dietary fiber correlated with microbiome composition

On last week’s podcast, we talked with Erica and Justin Sonnenburg about how the food we eat, and specifically dietary fiber, is important for “feeding” our microbiomes. All of the variables that influence microbiome composition are not fully understood, however research is continually being conducted to better understand what factors affect the microbiome.  To this end, a team of scientists from New York University School of Medicine set out to find how sex, body mass index (BMI), and dietary fiber intake impact the microbiome.

The scientists analyzed fecal samples from 82 individuals, 51 men and 31 women. They found that the women had different microbiome composition than the men, specifically a lower abundance of Bacteroidetes. They also found that BMI impacted microbiome diversity, specifically in women. Overweight and obese women had less diverse gut bacteria than normal weight women and women with a higher BMI also had less Bacteroidetes in their guts compared to the normal weight women.

The scientists also found that various sources of dietary fiber differentially impacted the microbiome of subjects.  Fiber intake from fruits and vegetables resulted in higher levels of Clostridia and fiber intake from beans was associated with greater abundance of Actinobacteria. It is possible that dietary fiber is influencing the microbiome by reducing gut transit time and lowering the pH. It is also possible that it is influencing systemic levels of estrogen, which could alter microbiome composition.

As the microbiome continues to be implicated in diseases, the ability to identify variables that affect the microbiome are important and can potentially be used for altering microbiota composition to prevent or possibly treat disease. 

How does a man’s seminal microbiome alter a woman’s vaginal microbiome?

There is very little research on the microbiome of semen.  We know that it is not sterile, and some scientists think that some of the bacteria found in semen may be involved in male fertility issues.  However, there is still a lot of research to be done in this area.  Even less is known about how the seminal microbiome influences the vaginal microbiome after sex.  Some research has suggested that specific sexual partners can cause bacterial vaginosis (BV), however the mechanisms for this are unclear.  It is suggested that perhaps the penile and seminal microbiome being transferred to the vagina during sex could cause this, although research has not confirmed these hypotheses.  Researchers from Estonia tried to answer these questions, and studied just how the vaginal and seminal microbiomes change before and after sex.  They published the results of their findings last week in Research in Microbiology. 

The scientists measured the seminal and vaginal microbiomes before and after sex for 23 couples who had sought help for infertility but were otherwise healthy.  They learned that the seminal microbiome, while containing much fewer bacteria, was actually more diverse than the vaginal microbiome.  Still though, each shared many of the same bacteria.  These included Lactobacillus, Veillonella, Streptococcus, Porphyromonas and Atopobium.  Interestingly, Gardnerella vaginalis, a bacterium highly implicated with BV, was found more frequently in women who had sex with men whose semen contained leukocytes, itself a phenotype associated with infertility.  While most of the women’s microbiomes did not shift after sexual intercourse, four of them did.  In these women a decrease in Lactobacillus occurred, and a decrease in Lactobacillus has also been highly implicated in BV.

While this study was preliminary, it marks some of the first research on the dynamics of the seminal and vaginal microbiome during sex.  The scientists suggest that the microbiome may be very important to fertility issues, and at the AMI we would not be surprised to learn that it is involved in at least some causes of infertility.  In the near future we will be devoting an entire podcast to the vaginal microbiome, and interviewing Jacques Ravel, a world leader in this field.  If you have any relavent questions and would like us to ask them on the podcast please call 518-945-8583 and leave your question on the voicemail.