The vaginal microbiota

The vaginal microbiota is an ecosystem constituted of microorganisms, where the genus Lactobacillus predominates. Its equilibrium is fragile and changes in its composition cause infections.

Vaginal microbiota, also known as Döderlein flora, has been described since 1894. It is a very complex ecosystem in dynamic equilibrium. Its composition varies widely from one person to another.^1-2

The predominant genus is Lactobacillus, which produces lactic acid that allows it to maintain a pH between 3.8 and 4.4 in normal conditions. This acidic pH creates a hostile environment for the proliferation of opportunistic pathogens.^3-5 Vaginal microbiota is a key factor in protecting the host against various bacterial, fungal, or viral pathogens. It also plays an essential role in the initial colonization of newborns, with consequences for the immune system and neurological development.⁶ The most commonly found species are L. crispatus, L. iners, L. jensenii, and L. gasseri. They offer antibacterial properties, produce biofilms, and promote the immune mechanisms that protect the vaginal mucus membranes.⁷

Besides the above-mentioned microorganisms, almost 250 bacterial species have been described, particularly anaerobic species like Prevotella, Gardnerella vaginalis, and Atopobium vaginae, but also Escherichia coli and the yeast Candida albicans.⁸ Their nature and concentration varies based on gene pool, ethnic origin, medication factors (antibiotics), environment, and behavior (sexual activity, personal hygiene, etc.), and are also influenced by the oral and intestinal flora.⁹

Vaginal microbiota changes over the lifetime (sexual hormones, menstruation, pregnancy, menopause, etc.) and these factors have an influence on the composition of this ecosystem.¹⁰

Although it varies from one woman to another, vaginal microbiota must maintain a certain equilibrium to preserve health in the reproductive tract.⁴  Various gynecological diseases can result from or be prompted by an imbalance in vaginal microbiota (dysbiosis), in particular bacterial vaginosis (A. vaginae, Clostridiales, and G. vaginalis) and candidal vulvovaginitis. The topical or oral administration of probiotics seems to promote an equilibrium in this microbiota, and may reduce symptoms in the case of vaginal infection as well as the likelihood of recurrence.

Sources
1- Hummelen, R. et al. Vaginal microbiome and epithelial gene array in post-menopausal women with moderate to severe dryness. PloS One 6, e26602 (2011).
2- Albert, A. Y. K. et al. A Study of the Vaginal Microbiome in Healthy Canadian Women Utilizing cpn60-Based Molecular Profiling Reveals Distinct Gardnerella Subgroup Community State Types. PloS One 10, e0135620 (2015).
3- Tomusiak, A. et al. Efficacy and safety of a vaginal medicinal product containing three strains of probiotic bacteria: a multicenter, randomized, double-blind, and placebo-controlled trial. Drug Des. Devel. Ther. 9, 5345–5354 (2015). https://www.ncbi.nlm.nih.gov/pubmed/26451088
4- Mizock, B. A. Probiotics. Dis Mon. 2015 ;61:259-90 https://www.ncbi.nlm.nih.gov/pubmed/25921792
5- Romero, R. et al. The composition and stability of the vaginal microbiota of normal pregnant women is different from that of non-pregnant women. Microbiome 2014; 2, 4
https://www.ncbi.nlm.nih.gov/pubmed/24484853
6- Dominguez-Bello, M.G.et al., Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proc. Natl. Acad. Sci. U.S.A. 2010; 107: 11971– 11975
7- A. Schwiertz (Ed). Microbiota of the Human Body. Advances in Experimental Medicine and Biology 2016; 902: 83-93 http://link.springer.com/book/10.1007%2F978-3-319-31248-4
8- Li J et al. Importance of vaginal microbes in Reproductive health. Reprod Sci 2012; 19:235-242 https://www.ncbi.nlm.nih.gov/pubmed/22383775
9- Pretrocevic L et al. Characterisation of the oral, vaginal and rectal Lactobacillus flora in healthy pregnant and postmenopausal women. Eur J Gynecol Reprod Biol 2012; 160:93-99.
https://www.ncbi.nlm.nih.gov/pubmed/22088236
10- Petrova, M. I. et al. Lactobacillus species as biomarkers and agents that can promote various aspects of vaginal health. Front. Physiol 2015;. 6: 81