The vaginal microbiome remained unexplored territory for a long time but in recent years it has become the subject to increased research. Thanks to the Human Microbiome Project scientists have come to know more about the bacterial composition in the vagina and how it varies from one woman to another. The microorganisms in the vagina live in symbiosis with their host and largely influence health.
Healthy women have many different kinds of microorganisms that live in the vagina. The composition and stability of the vaginal microbiome varies by race, age and even per individual.
In adolescence, the vaginal microbiome doesn’t look like that of a woman who has reached sexual maturity. A teenager’s vagina has less lactobacilli than an adult female’s. As you become more mature, your lactobacilli become the more dominant microorganism as they are there to protect you from infection.
Throughout your life and your menstrual cycle, the balance of bacteria is in a continual state of change. Amazingly enough, the composition of the vaginal microbiome can change in less than 24 hours. Some women have a more stable microbiome than others, and although we’re not entirely sure why this might be, we do know that friendly bacteria and fungi are constantly guarding your health.
During pregnancy for example, your vaginal bacterial balance undergoes a significant change as it prepares for birth. Even after the menopause, your microbiome continues to change and your levels of lactobacilli will start dropping again.
Often the dominant type of bacteria in the vagina is Lactobacillus, a lactic acid bacterium. This bacteria ferments carbohydrates into lactic acid. The fact that the vagina is an acidic medium can be explained by the presence of lactic acid bacteria. Although Lactobacillus is likely to be the most dominant bacterium in the adult vagina, there are lots more of these lactic acid bacteria to be found there. And with good reason.
The lactic acid in the vagina causes a higher level of acidity which pathogenic bacteria often cannot handle. Lactic acid bacteria are our first line of defence against infection. When the level of lactic acid bacteria in the vagina decreases, the degree of acidity becomes more neutral and the risk of infections increases. A sufficient amount of lactic acid bacteria in the vagina keeps a woman healthy.
Since these bacteria continually leave the body through vaginal secretions, lactic acid bacteria should be able to grow or proliferate. In order to support this bacterial growth, the host supplies nutrients to the microbial communities. Thus glycogen, excreted by the vaginal epithelial cells, provides a source of sugars for the lactic acid bacteria. This amount of glycogen may however decrease under the influence of hormonal changes, which in turn results in a decrease in lactic acid bacteria.
Composition according to race
One of the Human Microbiome Project’s studies states that the composition of the vaginal microbiome and the nature of the vaginal environment are related to race. 80 % of vaginal microbiomes amongst Asian women and almost 90 % amongst white women are dominated by Lactobacillus. Between Hispanic and black women this percentage was only 60%. The vaginal acidity level also differed by ethnicity. The pH of Asian and white women was between 4.4 and 4.2. Among Hispanic and black women, it was 5.0 to 4.7.
- Mirmonsef, P. et al., 2014. Free glycogen in vaginal fluids is associated with Lactobacillus colonization and low vaginal pH. PloS one, 9(7), p.e102467.
- Peterson, J. et al., 2009. The NIH Human Microbiome Project. Genome research, 19(12), pp.2317–23.
- Petrova, M.I. et al., 2015. Lactobacillus species as biomarkers and agents that can promote various aspects of vaginal health. Frontiers in physiology, 6, p.81.
- van de Wijgert, J.H.H.M. et al., 2014. The vaginal microbiota: what have we learned after a decade of molecular characterization? PloS one, 9(8), p.e105998.