Most of us are aware that useful micro-organisms reside in our gut but few of us would know that some microbes even colonize the vagina. Over 50 species of micro-organisms reside in the human vagina and maintain good health while preventing infections. These species do not remain constant throughout the lifecycle of a woman. Studies have shown that Lactobacillus species generally dominate the microbiota of healthy premenopausal woman; some of the common ones are L. iners, L. crispatus, L. gasserii, L. jenesenii, followed by L. acidophilus, L. fermentum, L. plantarum, L. brevis, L. casei, L. vaginalis, L. delbrueckii, L. salivarius, L. reuteri, and L. rhamnosus.

Factors that affect micro-organisms population in the vagina:

  1. Hormonal changes (particularly estrogen)
    Menstrual cycle changes the vaginal microbiota; high levels of estrogen, increase the adherence of the micro-organisms to the vaginal epithelial cells. Similarly, as menopause approaches and post menopause, estrogen levels drop, resulting in a decline in the lactobacilli of the vaginal tract. This makes the latter group more susceptible to urogenital infections.
  2. Vaginal pH
    The vaginal pH is acidic which is maintained by Lactobacilli that guard against any opportunistic pathogens. Vaginal douching, sexual practices (such as changing partners, use of oral contraceptives and intra uterine devices can change the pH of the vaginal and make it easier for pathogens to displace the healthy vaginal flora. The loss of lactobacilli is related to Bacterial Vaginosis that allows for growth of anaerobic bacteria, increases the pH (>4.5) and has also been associated with increased risk of sexually transmitted diseases, infertility, maternal infections and preterm birth. Antibiotic therapy could also contribute to a shift in the vaginal pH.
  3. Glycogen content
    Lactobacilli produce lactic acid that maintains the vaginal pH by metabolizing glycogen. The presence of glycogen has been associated with an acidic pH and proliferation of Lactobacilli. Nutrition or diet may also have an effect on the glycogen levels. In one study, women with a BMI≥30 had high levels of glycogen, however, this finding was only marginally significant.

While different species microorganisms coexist in the vagina, Bacteroides, Prevotella and Gardnerella are associated with bacterial vaginosis (BV), and E. coli and Enterococcus are associated with Urinary Tract Infections. G. vaginalis, a pathogen linked with BV was found coexisting with species of Lactobacillus in vaginal samples. Following an intravaginal lactobacilli instillation, G. vaginalis was displaced for 21 days beyond detectable limits. The micro-organisms in the vagina are believed to have the ability to modulate genetically controlled capacity of a microbe to kill other pathogens. In another study, L. rhamnosus GR- 1 administered to the vagina of premenopausal women aided the antimicrobial defences. Thus, there is a fine balance between the proliferation of microorganisms that can either contribute to good health or infections depending on various factors listed above. The outcome will vary based on which side the see saw tilts.

Antibiotics have been used to treat an overgrowth of undesired microorganisms in the vagina; however, with the increase in antibiotic resistant pathogenic microorganisms, the use of probiotics has been extensively considered. Yeast infections caused by Candida albicans, C. krusei, C. glabrata, and C. tropicalis as well as the bandwagon of Atopobium vaginae, Gardnerella vaginalis, Peptostreptococcus, Megasphera, Bacteroides, Mycoplasma hominis, Mobiluncus, and Prevotella that are responsible for BV, can be kept away with a the right probiotics everyday.


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  2. Lactobacilli Dominance and Vaginal pH: Why Is the Human Vaginal Microbiome Unique?
    Available from: https://www.frontiersin.org/articles/10.3389/fmicb.2016.01936/full
    [Accessed on 14 Feb 2018]
  3. Free Glycogen in Vaginal Fluids Is Associated with Lactobacillus Colonization and Low Vaginal pH.
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    [Accessed on 19 Feb 2018]
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    Available from: https://www.ncbi.nlm.nih.gov/pubmed/12265361
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    Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3758931/
    [Accessed on 19 Feb 2018]