Diverse inside and out: vaginal microbes differ with ethnicity?

Every time I read about a study on the microbiota composition whether it is from the gut, skin, or vagina, I wonder with which bacteria am I sharing my body. As a Peruvian researcher living in Belgium and now being involved in the Isala project, I also wonder about my vaginal microbiota composition and the ones from women like me: women with non-Belgian ethnicity but living in Belgium for several years. Perhaps our vaginal microbiota has changed over time and became similar to women with Belgian ethnicity? Or our ethnic background is “resisting” the possible Belgian environmental influence?

Now, probably you are asking yourself, what is ethnicity? Are ethnicity and race the same? Well the answers are complex. While ethnicity refers to cultural characteristics (e.g. language, accent, religion, social customs, food and dietary preferences or restrictions), race refers to physical characteristics that define a person as being a member of a specific group (e.g. skin/hair/eye color, physical build) (Sociologist Julie Maes, personal communication). From a scientific point of view, classifying individuals by their physical appearance lacks of validity, as demonstrated by genetic studies where the genetic differences within individuals of a certain “racial group” is higher than between “racial groups”1. From a social point of view, race is a category forged historically through oppression, slavery, and conquest2. Even though ethnicity and race have different meanings, they are usually used interchangeably.

Initial studies that gave the first insights on vaginal microbiota composition included only Caucasian women. These studies showed that the vaginal microbiota often was dominated by lactobacilli. Further studies conducted mainly in the United States included women from different ethnic groups showed that women from different ethnic background display a different healthy vaginal bacterial composition, with lactobacilli not playing the most prominent role3. Thus, it was found that the healthy vaginal microbiome of women from European ancestry are less diverse (dominated by Lactobacillus species) than those of African ancestry (non-Lactobacillus dominated)4. To the question ‘does a healthy vagina always needs to be dominated by Lactobacillus?’, more research is needed including different ethnic groups to understand what a “healthy vaginal microbiome” really means. However, apparently, we always need Lactobacillus species during pregnancy5. Interestingly, research has indicated that the presence of Lactobacillus species plays a positive role during pregnancy. Even more, the vaginal microbiome composition of pregnant women tends to be dominated by Lactobacillus species however it becomes less lactobacillus dominant during the post-partum irrespective of community structure during pregnancy and independent of ethnicity6. This makes the question on the relevance of the presence of lactobacilli even more interesting.

Why is there a difference? For the moment, the answers are unclear. Host genetics and environmental factors might contribute to the difference, however these factors don’t explain all of the variation seen in the vaginal microbiota of different ethnic backgrounds.

In the context of the Isala project, we aimed to include women from different ethnic groups, but because it is a Citizen Science project, we were unsure whether we could reach them. These uncertainties are common in research and several factors play a role for citizen participation7. Interestingly, based on the questionnaires, almost 11% of the participants, identify themselves with one or more culture(s) different from the Belgian one. Moreover, in terms of nationality, our project includes women from 99 different countries!  In this way, Isala’s volunteers are contributing to disentangle the effects of sociodemographic, behavioral, environmental, and genetic factors on vaginal microbiota composition.

We look forward to study the vaginal microbiome in other countries in collaboration with partner institutions, hopefully we will start a new Isala-like project in a multiethnic country like Peru, so fingers crossed!

Special thanks to Lore van Praag and Julie Maes for their help to verify the concepts of ethnicity and race.

References

  1. Rosenberg NA, Pritchard JK, Weber JL, et al. Genetic structure of human populations. Science 2002;298:2381-5
  2. https://genderedinnovations.stanford.edu/terms/race.html
  3. Ravel, J., P. Gajer, Z. Abdo, G. M. Schneider, S. S. K. Koenig, S. L. McCulle, S. Karlebach, R. Gorle, J. Russell, C. O. Tacket, R. M. Brotman, C. C. Davis, K. Ault, L. Peralta and L. J. Forney (2011). “Vaginal microbiome of reproductive-age women.” Proceedings of the National Academy of Sciences 108(Supplement 1): 4680-4687
  4. Serrano MG, Parikh HI, Brooks JP, et al. Racioethnic diversity in the dynamics of the vaginal microbiome during pregnancy. Nat Med. 2019;25(6):1001-1011.
  5. Romero, R., Hassan, S.S., Gajer, P. et al. The composition and stability of the vaginal microbiota of normal pregnant women is different from that of non-pregnant women. Microbiome 2, 4 (2014). https://doi.org/10.1186/2049-2618-2-4
  6. MacIntyre, D., Chandiramani, M., Lee, Y. et al.  The vaginal microbiome during pregnancy and the postpartum period in a European population.  Sci Rep 5, 8988 (2015).
  7. Redwood, S., & Gill, P. S. (2013). Under-representation of minority ethnic groups in research–call for action. The British journal of general practice: the journal of the Royal College of General Practitioners, 63(612), 342–343.

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