New probe developed to detect specific bacteria associated with bacterial vaginosis

Confocal laser scanning images with 400x magnification of G.vaginalis biofilm in 2 vaginal slides (A and B) in a superimposed image: vaginal epithelial cells in blue and G. vaginalis specific PNA-probe in red. A: vaginal sample with dispersed bacteria; B: vaginal sample with bacteria in biofilm.

Bacterial vaginosis (BV) is a topic we have previously covered on the blog, because of its significance to women’s health. BV is a change in women’s vaginal bacterial composition, in which bacteria that are usually associated with health are at a decreased presence in comparison to BV-associated bacteria. BV is such an issue because it causes a biofilm to form that increase susceptibility HIV and other sexually transmitted infections. BV also has negative effects on pregnancy and is a threat to women of reproductive age. Clearly this is an important topic of research, and was the focus of an article recently published by PLOS ONE.

BV is usually characterized by the presence of Gardnerella vaginalis and Atopobium vaginae. A.vaginae has previously been shown to be much more common than G. vaginalis in BV patients. In the PLOS ONE study, researchers focused on finding the best way to detect these two bacteria in vaginal samples. Samples were taken from 119 women in Rwanda, between the ages of 18 and 35 years old. After testing multiple different probes that had been developed by the researchers, they found that something called the PNA FISH is a very good tool for detecting bacteria in biofilms. Through this study the scientists were able to detect that higher quantities of G. vaginalis and A. vaginae are associated with bacterial biofilms. Almost half the samples containing G. vaginalis also contained A. vaginae, whereas all of the samples that contained A. vaginae were also positive for G. vaginalis.

With the data collected, the researchers hypothesize that G. vaginalis is a main cause of vaginal biofilms when it is high enough in concentration. Hopefully with the discovery of effective probes, much more can be discovered about bacterial vaginosis.    

Bacterium identified that may be associated with cervicitis

Cervicitis is an inflammation of the uterine cervix of women. This condition is known to be associated with many different infections, such as Chlamydia trachomatis or Neisseria gonorrhoeae, however the true cause of the inflammation is still unclear. Researchers in Seattle, Washington performed a study, recently published by the journal Sexually Transmitted Diseases, to determine whether it is an imbalance of the vaginal and/or cervical microbiome that is at the root of the problem. The study’s aim was to look at the associations of bacteria with cervicitis in two different groups of women, to see if the results of each group agree.

At a clinic in Seattle, vaginal and cervical samples were collected from a group of predominantly young white women that agreed to the study. Of the 210 women from the clinic, only 14 were identified as having cervicitis based on certain identification criteria. A parallel control study was performed in Mombasa, Kenya with the hopes that the gathered information would either refute or confirm the results of the Seattle group. The Seattle results showed that women with cervicitis were more likely to have Mageeibacillus indolicus in the cervix and vagina than women without the condition. The bacteria Lactobacillus jensenii was the only species that was more present in women without than with cervicitis.

The Kenyan study did not show that M. indolicus was more present in women with cervicitis. In fact, the bacterium was more common in women without the condition. While the results of this study are confusing, because the Kenyan study seems to disprove the results of the Seattle study, it important to keep in mind the flaws of this study as a whole. There were many factors not taken into consideration during analysis, such as birth control intake and viral infections. Additionally, the criteria of cervicitis diagnosis were most-likely different in Seattle and Kenya, and there were very few women in the study that even had the condition. Regardless of the flaws, this study still gave good results which could lead scientists too look further into M. indolicus and L. jensenii for their contribution to cervical health. 

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.

New research helps determine what is healthy and unhealthy in the vaginal microbiome

Editor’s note: This blog about the vaginal microbiome is a good primer for this coming Monday’s Microbiome Podcast with Jacques Ravel, where we will discuss the vaginal microbiome and women’s health at length.  There will also be a special announcement during this podcast, so anyone interested should be sure to download it Monday, June 1.

The typical ‘healthy’ vaginal microbiome is dominated by a Lactobacillus.  However many women, especially those of African descent, are not dominated by this genus, and instead have a high diversity of bacteria in their vaginal tract.  This low lactobacilli, high diversity phenotype has been associated with many disease states, such as bacterial vaginosis (BV), preterm birth, and higher rates of sexually transmitted disease (STD) transmission.  (We have written about some of these diseases before, and encourage any interested reader to click the ‘vaginal microbiome’ below this story to learn more.)  Vaginal microbiome research is still in its early days though, and it is not clear why vaginal microbiome not dominated by Lactobacillus should lead to these diseases, and if this phenotype, if asymptomatic, should even be considered unhealthy.  New research though, out of Harvard University, shows that this phenotype does lead to inflammation, and that these inflammatory response can affect reproductive health and STD transmission.  They published their study in the journal Immunity last week.

The scientists studied the vaginal microbiomes of a cohort of 146 HIV negative, asymptomatic, black, South African women.  They discovered that 63% of them were not dominated by Lactobacillus, an extremely high percentage, especially compared to their counterparts in developed countries (38% of black women and 10% of white women).  Nearly half of those women were dominated by Gardneralla vaginalis, which is most commonly associated with BV, and a large percentage of the other half were diagnosed with BV after investigation.  This is especially interesting because, as stated before, all of the women in the cohort claimed to be asymptomatic, but as we are learning, many women are unaware that there is anything wrong.  Overall, the women were able to be grouped into 4 specific phenotypes, those dominated by Lactobacillus iners, those dominated by other Lactobacillus crispatus, those dominated by Gardnerella vaginalis, and those with a high diversity including Gardnerella vaginalis, Fusobacterium gonidiaformans, Prevotella bivia, and Atopobium vaginae (note the lack of Lacotbacillus in this high diversity group). 

The scientists discovered that there were no associations between each vaginal microbiome group and the rate of STDs, contraceptive use, or sexual behavior.  This is important in showing that, at least on first pass, these bacterial communities were not the result of these exogenous factors (nor did they cause them, for that matter).  They also discovered that there was only a loose association between inflammatory cells in the vaginas of these women, and whether or not they had an STD.  The loose association was only observed in women with Chlamydia, and the women with the highest levels of inflammation had no apparent STDs.

The fact that STDs were not strongly associated with inflammation led the researchers to hypothesize that the vaginal microbiome community, rather than STDs, were responsible for vaginal inflammation.  Indeed, when they compared the amount of inflammatory cells in each vagina with the different microbiome groups described earlier, they found a strong association between inflammation and the highly diverse microbiome group.   Moreover, when they tracked individual women over time, those women whose vaginal microbiomes shifted to the high diversity group also increased inflammatory responses.  The researchers then took this work a step further, and identified specific bacteria that were associated with the inflammatory response:  Prevotella amnii, Mobiluncus mulieris, Sneathia amnii, and Sneathia sanguinegens.

Finally, the researchers measured genes for specific receptors in the vagina that are known to trigger an immune response.  They discovered that those women with the high diversity vaginal microbiomes upregulated genes for these receptors, which are known to be activated by bacteria.  Making matters worse, specific immune cells that are triggered by these receptors, which are thought to be critically important to HIV transmission, were found in higher abundances in women in the high diversity vaginal microbiome group.

This paper did a really great job showing that a vaginal microbiome that lacks Lactobacillus is indeed an unhealthy state, because it creates a highly inflammatory vaginal microbiome which likely causes or contributes to many other ailments, beyond just the higher rates of HIV transmission that was demonstrated.  Unfortunately, at the moment, there are no easy ways for women to check which vaginal microbiome they have, but that should be changing soon, and we recommend that all of our readers tune into the Microbiome Podcast this coming Monday to hear a big announcement in this area.