The vaginal microbiome represents one of the primary locations for microbiota within the female body, and is predominantly populated by Lactobacillus species, which include Lactobacillus crispatus (L. crispatus), Lactobacillus gasseri (L. gasseri), Lactobacillus jensenii (L. jensenii), and Lactobacillus iners (L. iners). Vaginal microbiota plays a crucial role in safeguarding the vaginal ecosystem and significantly affects various aspects of health, including immune function and human development.  

Many factors influence the diversity of vaginal microbiota, including access to healthcare, cultural practices, diet and lifestyle, genetics, hormone balance, hygiene habits, and the use of medications. Consequently, each individual has distinct characteristics in their vaginal microbiota composition. 

Development of the vaginal microbiome can be attributed to bacterial translocation from the gastrointestinal tract to the vaginal region or through maternal transmission during vaginal delivery. Consequently, the gut-vagina axis is established with lactobacilli and other bacterial strains communicating between the gut and vagina, closely regulating both local and systemic immune responses.

The beneficial role of short-chain fatty acids — primarily acetate, propionate, and butyrate — in the gut microbiota is well established. SCFAs are fundamental for overall health, performing vital functions related to metabolism, immunity, and nutrient absorption. Synthesized by gut microbes from dietary fibers, they exert immunomodulatory effects by maintaining the intestinal barrier's structural integrity and enhancing tight junction protein function. By reducing intestinal permeability, SCFAs play a protective role in mitigating systemic inflammation.

In contrast, the physiological role of vaginal microbiota-associated SCFAs is less well understood. Research suggests that elevated levels of SCFAs in the vaginal microbiome may disrupt the balance between commensal and pathogenic bacteria. This imbalance can lead to inflammation, infections, decreased Lactobacillus populations, reduced lactic acid production, increased vaginal pH, and a higher relative abundance of mixed anaerobes. Additionally, the translocation of gut microbial species to the vagina, coupled with increased SCFA production, can adversely affect vaginal microbiota composition. These findings underscore the importance of maintaining a Lactobacillus-dominated vaginal microbiota.

Research associating gut dysbiosis and estrogen metabolism to female reproductive disorders like bacterial vaginosis (BV), endometriosis, and polycystic ovarian syndrome, further elucidates the robust connection between the gut and vaginal microbiomes. The estrobolome, the microbiome associated with estrogen metabolism, is influenced by gut dysbiosis, which reduces β-glucuronidase activity and impacts the body’s ability to metabolize circulating estrogen and phytoestrogens. Hypoestrogenic conditions may increase the risk of obesity, metabolic syndrome, and cardiovascular disease. Alternatively, increased levels of β-glucuronidase-producing bacteria may induce a hyperestrogenic effect, contributing to conditions such as endometriosis. Improving the gut microbiome with a balanced, fiber-rich diet will further support the homeostasis of vaginal microbiota.

The Role of Lactobacillus species in the Vaginal Microbiome

Approximately 70% of women exhibit Lactobacillus spp. as the predominant bacterial strain, which is recognized as a favorable biomarker for vaginal health. In a cohort analysis of 3,196 vaginal microbiome samples, the Lactobacillus genus was identified as the most predominant, with L. crispatus accounting for 43.2%, L. jensenii comprising 3.5%, and L. gasseri representing 3.2% of the total microbiota. 

The absence of a Lactobacillus-dominated vaginal composition does not automatically signify dysbiosis or disease. However, an increased diversity of non-Lactobacillus species might affect the vaginal pH balance by lowering lactic acid levels, which could create a more favorable environment for pathogenic bacteria to thrive and potentially promote unbalanced immune and inflammatory responses. 

The composition of the vaginal microbiome typically shifts throughout the menstrual cycle and during various life stages, such as pregnancy, postpartum, and menopause, due to fluctuations in estrogen. Studies show that during menstruation, there can be up to a 100-fold decrease in L. crispatus and an increase in other bacterial strains, including L. iners, Prevotella bivia, and Gardnerella vaginalis, due to reduced estrogen levels. Elevated pH levels during menstruation foster an environment conducive to pathogenic bacteria proliferation, potentially resulting in aerobic and bacterial vaginitis, characterized by symptoms like vulvovaginal irritation, itching, or burning. With a common recurrence rate, bacterial vaginosis (BV) can play a detrimental role in overall fertility and pregnancy-related outcomes. Large cross-sectional studies indicate that pregnant women with BV face an elevated risk of premature birth, ranging from 40% to 84% compared to those without BV. Research indicates that oral and vaginal probiotics can improve overall vaginal health by promoting the growth of lactobacilli.

Probiotic Strains Supporting Vaginal Microbiome Health

Probiotic supplements play a crucial role in promoting vaginal microbiome health, as well as enhancing gastrointestinal function and supporting a healthy immune response. Some species of  Lactobacillus are widely recognized for their properties associated with the production of lactic acid, with proven efficacy against pathogens in both the vagina and gastrointestinal tract, including L. crispatus, L. jensenii, L. gasseri, and  Lactobacillus rhamnosus (L. rhamnosus). Each lactobacilli strain has unique mechanisms of action that positively contribute to overall vaginal health. 

The abundance of L. crispatus has been identified for its role in maintaining homeostasis in the vaginal microbiome. Positively associated with the luteal phase of the menstrual cycle, it possesses antagonistic activity against opportunistic pathogens in both vaginal and gut microbiota. 

A citizen-science study (N = 3,345) investigated how dietary and lifestyle choices relate to vaginal microbiota diversity. Lower levels of L. crispatus were connected to sugary beverages and meat consumption, while a higher intake of vegetables and fiber correlated with increased L. crispatus levels. Using vaginal probiotics as a short-term intervention (for three to 10 days) to restore vaginal health resulted in persistent colonization of L. crispatus in 44% to 59% of women.  

Co-occurrence patterns have been identified between L. crispatus and L. jensenii, which contribute to the stimulation of innate immunity. This observation suggests that the combination of both strains in a probiotic supplement may offer synergistic support for the vaginal microbiome. L. jensenii and L. gasseri also exhibit biosurfactant properties, which may offer anti-adhesion effects against pathogenic bacteria with biofilms, including Candida albicans and Escherichia coli.

Researchers assessed the impacts of prescribed antibiotic medication compared to adjuvant probiotic treatment of vaginal microbiota levels in a parallel controlled trial involving 67 women diagnosed with BV. Women who took oral probiotics containing L. gasseri and L. crispatus for 30 days experienced a restorative effect on their vaginal microbiome, supporting the unique ability of these strains to support bacterial balance and overall vaginal health. Additionally, pregnant women (n = 32) receiving oral supplementation of L. rhamnosus and Lactobacillus reuteri twice daily for 12 weeks exhibited reduced recurrence of BV and urinary tract infections, which helped to replenish vaginal lactobacilli during pregnancy. 

Ultimately, maintaining a healthy vaginal microbiome is vital for reproductive and urogenital health. Lactobacillus probiotics play a key role in supporting this balance by producing lactic acid, lowering vaginal pH, and inhibiting the growth of harmful pathogens. Incorporating Lactobacillus-rich probiotics through diet, supplements, or targeted therapies can help restore and sustain a resilient vaginal microbiome, reducing the risk of infections and promoting long-term wellness.

To learn more about the vaginal microbiome and probiotic support:

The Immunomodulating Effects of Lactobacillus Rhamnosus GG

Supporting the Vaginal Microbiome: The Why and How

Vaginal Dysbiosis and the Supportive Role of Probiotics

By Rachel B. Johnson, MS, CNS, LDN