Lactobacillus Species and Vaginal Defense Mechanisms

Lactobacillus species defend the vaginal mucosa by producing lactic acid, maintaining a pH of 3.5–4.5, and releasing bacteriocins and hydrogen peroxide, which hinder pathogen growth. They thrive in anaerobic conditions, regulating the acidic environment to deter pathogens. Lactobacilli also form microcolonies, competing with pathogens for nutrients, and modulate the immune system, suppressing proinflammatory cytokines. Overall, their multifaceted actions maintain vaginal homeostasis and protect against infections..

Impact of Vaginal Microbiome on Fertility and Pregnancy

The vaginal microbiota also regulates immunological function and inflammation locally, and eubiosis has been correlated with several beneficial actions. In the context of fertility and pregnancy, the maternal immune system must balance protection against pathogens and tolerance toward pregnancy and commensal flora, necessitating bi-directional interaction with the microbiome. An abnormal vaginal microbiome (dysbiosis) is associated with dysregulation of the above-mentioned beneficiary effects, resulting in reproductive system pathology, including bacterial vaginosis.

Vaginal microbiome is linked with Infertility

Lactobacillus-dominated vaginal flora is typically associated with normalcy, while bacterial vaginosis-linked microbiomes are implicated in infertility among women of reproductive age. Studies show that women experiencing unexplained infertility are more likely to exhibit abnormal vaginal flora. In vitro research underscores the vaginal microbiome's significance in embryo implantation and pregnancy outcomes, particularly with hydrogen peroxide-producing L. crispatus, which enhances implantation rates and live birth while mitigating adverse pregnancy outcomes.

Vaginal microbiome and Preterm Birth

Furthermore, abnormal vaginal flora poses a potential risk factor for preterm birth, with Lactobacillus-abundant flora significantly reducing this risk. In the first trimester, women with Lactobacillus-dominated flora exhibit a 75% lower risk of preterm delivery compared to those with flora characterized by bacterial vaginosis-associated bacteria colonization. Moreover, women harboring multiple Lactobacillus species had a lower risk of preterm delivery than those with only one species. Notably, Lactobacillus iners predominance was linked to preterm birth risk in pregnant women.

Impact of Bacterial Vaginosis on Infertility and Pregnancy

Studies show that bacterial vaginosis is prevalent in infertile women, with reduced conception rates observed compared to fertile counterparts, underscoring the importance of abundant Lactobacillus species for a healthy vaginal flora. Bacterial vaginosis disrupts the vaginal microbiota by reducing protective Lactobacillus species while increasing facultative and anaerobic organisms. This imbalance is linked to adverse outcomes such as preterm birth and low birth weight. Overgrowth of anaerobes like Gardneralla vaginalis, Mycoplasma hominis, and Ureaplasma spp. among others, cause a pH imbalance and have been linked to infertility and recurrent implantation failure (RIF). Bacterial species such as Prevotella, Atopobium, Gardnerella, Megasphaera, and Mobiluncus have been associated with abnormal vaginal microbiota in asymptomatic reproductive-age women.