Understanding the Vaginal Microbiome

What should a healthy vagina look like?

The vaginal microbiome is a specialized microbial community that plays a crucial role in maintaining vaginal health and fertility. It consists of various microorganisms, with bacteria being the most prominent. A healthy vaginal microbiome in general is a microbiome dominated by Lactobacillus species. Lactobacillus organisms produce lactic acid, which keeps vaginal pH at 3.8-4.5.

While it’s essential to recognize that various bacterial organisms can dominate the vaginal microbiome, it appears that lower bacterial diversity is preferable. Despite the presence of some women with low levels of lactobacilli who remain asymptomatic, the health status of such individuals remains a topic of scientific discussion. However, research indicates that women with decreased number of Lactobacillus species in their vaginal microbiome are more vulnerable to vaginal infections, as their microbial balance can be easily disrupted by pathogens.

The most important bacterial species in the vaginal microbiome are:

Lactobacillus crispatus

• present in 65% of women universally
• dominates vaginal microbiome of up to 45% of women
• the most beneficial Lactobacillus species
• creates stable colonies
• produces the highest quantities of lactic acid
• dominates healthy and stable vaginal microbiome
• unlikely to transition to BV microbiome state
• more likely to transition to L. iners dominant microbiome

Lactobacillus iners

• the second most common bacteria in a healthy vagina
• moderate lactic acid production
• associated with both normal and abnormal microflora
• transitional species
• can coexist with pathogenic organisms as it either adapts to higher pH conditions or it is more resistant to unfavourable growth conditions
• higher quantities could indicate that the vaginal microbiome is transitioning toward disruption and imbalance
• less protective against pathogens

 Lactobacillus gasseri

• present in more than 40% of women
• dominates vaginal microbiome of 5-8% of women
• produces powerful antimicrobial bacteriocins
• rare transition to other communities

Lactobacillus jensenii

• beneficial Lactobacillus species
• moderate lactic acid production
• not permitted to be used in medical products in Australia

Here are some key factors that influence the composition and dynamics of the vaginal microbiome:

1. Estrogen levels. Higher estrogen levels stimulate production of glycogen by vaginal epithelial cells. Glycogen serves as a food source for Lactobacillus bacteria. Therefore, higher estrogen levels promote the growth of Lactobacillus species.
2. Menstrual cycle phases. During menstruation estrogen levels are low, and vaginal pH becomes more alkaline. This transiently reduces Lactobacillus numbers, allowing other bacteria to thrive and bacterial diversity to increase. Post-menstruation, as estrogen levels rise, Lactobacillus populations recover.
3. Pregnancy. Pregnancy is associated with high estrogen levels. The vaginal epithelial cell layer thickens, providing additional protection. Lactobacillus species dominate during pregnancy, contributing to a stable and protective microbiome.
4. Menopause. With declining estrogen levels during menopause, the vaginal environment changes. Reduced glycogen availability, thinning of vaginal wall cells, and decreased Lactobacillus colonies can lead to an altered microbiome.

Summary of vaginal health parameters throughout a women’s lifespan are given in the table below.