January 2024
Dr. Kim Capone, Lead SHWI Educator, and Chief Science Officer for Vaginal Biome Science.
As the Chief Science Officer at Vaginal Biome Science it is gratifying to witness the significant uptick in research and scientific interest in the importance of the vaginal microbiome. In December, Scientific American published the article, “The Vaginal Microbiome May Affect Health More than We Thought” (https://www.scientificamerican.com/article/the-vaginal-microbiome-may-affect-health-more-than-we-thought1/), that summarized a recent peer-reviewed publication by Johanna Holm et al. from Jacques Ravel’s lab https://rdcu.be/dvrAB.
The Scientific American article provided an excellent overview of the many common conditions associated with a dysbiotic vaginal microbiome and the far-reaching consequences. It also highlighted the focused research to identify the composition and function of vaginal microbiota in health and disease by many researchers across the field. When reading the peer-reviewed paper, I was struck by the authors’ comment “Critically, these data support the need for an improved definition of BV, and the importance of a personalized approach.” This comment speaks to the many aspects of bacterial vaginosis that remain a mystery to many practitioners and patients alike.
Bacterial vaginosis (BV) is the most common cause of vaginal discharge and is often termed an infection, with a global prevalence ranging between 23-29%. This percentage is even higher in Black (33.2%) and Hispanic (30.7%) women. Although BV is not considered a sexually transmitted infection, the role of transmissibility has not been fully explored. Historically, bacterial vaginosis was thought to be caused by Gardnerella vaginalis, but newer data show this is not the only BV-associated organism. Thus, BV is perhaps better explained as a polymicrobial imbalance in the vaginal microbiome. Qualitatively we know that BV can be described as typically caused by a decrease in the number of normal hydrogen peroxide-producing lactobacilli with an overgrowth of anaerobic bacteria. However, as Dr. Holm comments, a personal approach to treatment is important because the manifestation of symptoms and the microbial communities associated with disease may differ significantly between individuals.
Why some women have a more resilient vaginal microbiome vs. others is beginning to be better understood with recent findings, but many unknowns remain. Previous studies have shown that there exist combinations of multiple strains of the same species in a vaginal microbiome of any community state type (CST). This complexity of microbes is essential to define and understand as some of these strains may encode functions in their genomes that allow them to take advantage of the environment to cause BV symptoms, while other strains of the same species do not cause these vaginal health issues.
Further refining the CSTs into subclasses based on the strains of the various species and their abundances in the vagina is an important evolution in the research. One of the most prevalent types of lactobacilli in women, L. iners, which predominates the vaginal microbiome in CST III, has been long associated with an increased risk of BV. However, there are exceptions, so the role of L. iners in vaginal health is still debated. The refined CST classifications provide novel insights into the role of L. iners as there are strains of L. iners associated with BV and others that are not – providing the first evidence of genetically distinct strains of L. iners that likely perform differently in the vaginal ecosystem.
Likewise, the study also found that having a wider variety of Gardnerella strains in a microbiome increased the risk of BV, likely due to the interactions and functions across strains within this species, and with other organisms in the microbiome. While this work was all done in reproductive age women, it’s very common for the vaginal microbiome of menopausal women to be dominated by Gardnerella, many without any BV symptoms. Clearly a new direction of work to define and describe the strain level composition of various Gardnerella-dominated menopausal microbiomes is needed.
Although it has been 17 years since the first vaginal microbiome samples were collected for the Human Microbiome Project, we remain limited in our understanding of the ways in which the various combinations of species and strains of microbes impact the function of the microbiome. Given the growing concerns over antibiotic resistance, and the persistent use of antibiotics as a mainstay in the standard of care in the most common vaginal conditions, including BV, we must take this challenge seriously and find alternative approaches to restoring and maintaining vaginal microbiome stability.