Vaginal microbiome once again tied to preterm birth

Preterm birth is major global health challenge.  Today, around 11% of all babies are born prior to 37 weeks, and are considered preterm.  Many of the causes of these preterm births are still unknown, but it is thought that around 25% of them may be related to a bacterial infection that comes from somewhere in the mother’s own body, i.e. her microbiome.  Many studies are now linking specific vaginal bacteria to risk of preterm birth, and other studies have even shown a connection between other microbiome sites, such as the gut and oral microbiome.  Unfortunately, studies on the microbiome and preterm birth are extremely difficult to conduct, so there are just not enough to have any sort of scientific consensus on the topic.  Last week though, a very rigorous study out f Stanford University was published in the Proceedings of the National Academy of Sciences that monitored expectant mothers vagina, gut, and oral microbiome throughout the course of her pregnancy and then for one year after.  Among many interesting findings, which are discussed below, the most important one was yet another connection between bacterial vaginosis and preterm birth.

The researchers monitored the vaginal, distal gut, salivary, and tooth/gum microbiomes of 49 women, 15 of which ended up delivering preterm, over the course of their pregnancy and for one year after.  Interestingly, the non-vaginal sites’ microbiomes remained relatively stable over the duration of the pregnancy, and even for the one year after.  The vaginal microbiome, however, did show some differences during and after pregnancy.

As many of our readers already know, a healthy vaginal flora is dominated by Lactobacilli, but around 20% of American women are dominated by other species, such as Gardnerella vaginalis, and have an overall increased vaginal diversity.  These women have what is known as community state type four, or CST4, and these women could be diagnosed with bacterial vaginosis (BV), though the clinical diagnosis is not so specific.  The other community state types, CST1, 2, 3, and 5, are dominated by different strains of Lactobacilli, and are generally regarded as healthy.  This current research showed that many of the women’s vaginal microbiomes actually shifted between various CST’s during pregnancy, most often shifting to and from CST4.  These transitions had no association with preterm birth, though.  After giving birth the vaginal microbiome became more diverse, and had greater abundances in anaerobic bacteria, such as Peptoniphilus, Prevotella, and Anaerococcus.  In addition, this usually coincided with a decrease in Lactobacilli.  Surprisingly, these changes did not seem to relate to mode of delivery (C-section of vaginal).

CST4 has been linked to preterm birth before, and this was reinforced in this study.  The scientists found that the longer a women’s vaginal microbiome was within CST4, the greater risk she had for preterm birth.  In addition, the abundance of Gardnerella and Ureaplasma, specifically, were linked to preterm birth.

This study reinforces what many microbiome scientists already suspect, and that is the importance of the vaginal flora in preterm birth.  It is unclear at this point if manipulating the vaginal flora prior to, or during pregnancy would help prevent preterm birth, but it is certainly worthy of discussion and clinical testing.  If you are reading this and wondering what your vaginal microbiome is, then we recommend you participate in the citizen science project, YourPrivateBiome, to find out.  You can learn more about it by following this link on our site, or just click the link above.

Bacterial vaginosis associated bacteria may increase a women’s risk for miscarriage

Bacterial infections or even slight imbalances can be damaging at many difference locations in the human body. One that should be taken seriously in bacterial vaginosis, which is an infection in females where a healthy bacterial balance is taken over by bacteria such as Gardnerella vaginalis, Ureaplasma urealyticum, and Mycoplasma hominis to name a few. Meanwhile, the presence of Lactobacillus crispatus and Lactobacilus iners would be characteristic of a normal vaginal microbiome. In a study out of Philidelphia, Pa that was recently published by Maternal and Child Health Journal, researchers inspected a possible connection between bacterial vaginosis and pregnancy miscarriages.

          A total of 418 pregnant women were included in the study. 65% of the women were African American, 27% were Hispanic, and 4% were Caucasian. Women were eligible if they were seeking treatment prior to 14 days of gestation, if they were not pregnant with multiples, and if there were no issues in terms of ectopic or molar pregnancy. Swabs were collected from the women and analyzed. During this study, 74 women experienced a miscarriage, while 344 delivered at term.

          It was found that the group of women who had miscarriages were older than those who did not. Women with high concentrations of Bacterial Vaginosis-Associated Bacterium 3 (BVAB3) before 2 weeks gestation had a 20% increased chance of miscarriage. On the other hand, for each one unit increase in Leptotrichia/Sneathia species concentration, risk of miscarriage decreased by 20%, and for that of Megasphaera phylotype 1-like species risk decreased by 19%. The implications of this type of research could be very beneficial to women everywhere. More knowledge like this could hopefully one day lead doctors towards even better care for pregnant women. Ideally, with more research into this area, the prevalence of miscarriages could be lowered. 

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.