Recurrent Bacterial Vaginosis: A Review of Current Treatments and H₂O₂-Producing Lactobacillus as a Probiotic for the Vaginal Microbiome

Introduction 

The vaginal microbiome plays a crucial role in a woman's physical and mental health. Today, one of the most common reasons for vaginal microbiome imbalance, or vaginal dysbiosis, is Bacterial Vaginosis (BV) [1]. Many studies show that recurrence of BV is very common after antibiotic use, with recurrence rates as high as 69% within 12 months of treatment [1]. The treatment options that physicians currently have are limited in supporting the overall health of the vaginal microbiome and largely consist of non-selective antibiotics [1]. Antibiotics often serve as a temporary fix, sometimes even contributing to BV recurrence [16]. While antibiotics remain the primary treatment for BV, some physicians are beginning to advocate for probiotics to help restore eubiosis in the vaginal microbiome [1,12,13,14,16]. As a result, scientists have recently conducted studies on different strains of Lactobacillus and the integral role they play in balancing the vaginal microbiome [4,5,6,12,13,14,16]. One promising treatment, Lactin-V, a strain of Lactobacillus crispatus, has been studied as a suppository probiotic, showing promising results thus far [1,12,13,14,15,16]. This review will discuss why supplemental Lactobacillus probiotics, with its natural protection and H2O2 production, should be integrated into the standard treatment of antibiotics for women with recurrent BV to combat its negative health impacts. 

Background 

The vaginal microbiome has three main groups of inhabitants: beneficial bacteria, harmful bacteria, and fungi which coexist in most healthy vaginas. The “good” bacteria are typically some form of lactic acid bacteria (LAB), primarily Lactobacillus species, which maintain a protective environment with an optimal pH of 4-4.5 [6]. The “bad” bacteria are most often Gardnerella vaginalis. G. vaginalis overgrowth leads to Bacterial Vaginosis (BV) and increased inflammation in the vagina (~pH 5-6.5) [6]. The fungus Candida albicans is responsible for most yeast infections, with a broader pH range (~2-10). G. vaginalis and C. albicans do not have negative effects in the vagina when they exist in small amounts, but if either overgrow they can disrupt the delicate balance of the vaginal microbiome. To prevent this overgrowth, vaginal Lactobacillus has a multifunctional protective role, preventing overgrowth of  G. vaginalis and C. albicans. It is not fully understood how it does this, but scientists believe that it maintains the vaginal pH and that its metabolites, Lactic Acid and H2O2, also help maintain the microbiome’s homeostasis. 

The current standard of treatment for BV and yeast infections are antibiotics and antifungals, respectively. Unfortunately, antibiotics are non-selective and often kill Lactobacillus in addition to G. vaginalis. After the Lactobacillus in the vagina is depleted, it is very hard to reestablish its dominance in the microbiome, leading to vaginal dysbiosis. Current antibiotic treatments often trigger a cycle of recurrent infections of either recurrent BV and/or yeast infections. 

Recurrent Bacterial Vaginosis’ Negative Impacts on Health 

In the vaginal microbiome, Lactobacillus plays a key role in maintaining eubiosis (microbiome balance) [2]. Many studies from the past few decades show that women with a Lactobacillus-rich microbiome have a lower risk of acquiring bacterial and viral infections than women whose microbiomes are dominated by pathogenic bacteria [1,2,3]. Many women that have taken antibiotics or have other risk factors have decreased Lactobacillus presence in their microbiome. This decrease in Lactobacillus frequently leads to domination by G. vaginalis instead of Lactobacillus, leading to BV [1,10]. BV has serious impacts on a woman’s physical and mental health [1]. In one study, 83.9% of respondents experienced vaginal odor, 82.3% had irregular vaginal discharge, and 67.7% dealt with vaginal irritation/itchiness [1].  71% of women reported that their BV negatively affected their sex life and 75.8% said that it impacted their mental health [1]. Many of the participants had also tried alternative products (including boric acid, folic acid, cranberry juice, intravaginal probiotics, Vagasil, coconut oil, hydrogen peroxide, yogurt, garlic, vinegar, and rephresh gel) because their BV was negatively impacting their quality of life [1]. Studies have also shown that BV can increase risk for cervical lesions, preterm birth, pelvic inflammatory disease, and HPV, which leads to cervical cancer in women [1,2,6]. In addition, G. vaginalis adheres to the vaginal epithelium and promotes the development of BV [1,2,4]. It is widely accepted and understood that biofilms in BV are caused by G. vaginalis overgrowth and that these residual biofilms are a main reason why antibiotics frequently lead to BV recurrence [1,4]. BV’s natural enemy is Lactobacillus domination in the vaginal microbiome because it has antagonistic effects to counteract G. vaginalis’ epithelial adherence and biofilm formation through competitive rejection [2,4]. This means that the Lactobacillus and G. vaginalis’  are in direct competition with one another and whichever grows more effectively will survive and inhibit the growth of the other. This mechanism of action has only been investigated recently, which is why there are limited vaginal Lactobacillus probiotics available today. 

Mechanism of Action between Lactobacillus and G. vaginalis 

Many strains of Lactobacillus have been studied extensively in vitro to learn more about their mechanism of action. In a study by Qian et al., three Lactobacillus strains were shown to outperform G. vaginalis in epithelial cell adhesion and H₂O₂ survivability. Epithelial cell adhesion is important to study because when bacteria adheres to the epithelial cells it is much more likely to survive in that environment. H₂O₂ survivability was studied because the vaginal microbiome can naturally produce H₂O₂, meaning the ideal environment would contain H₂O₂. The best strains of protective bacteria should be able to survive in a H₂O₂ environment. Since the study showed that the Lactobacillus outperformed the G. vaginalis, this means that theoretically the strains of Lactobacillus should be able to outsurvive the G. vaginalis and thus protect the vaginal microbiome. Inhibition of G. vaginalis growth also reached an impressive 98% [4]. While fewer studies have been conducted in vivo, a small study involving five participants with a history of recurrent BV demonstrated that vaginal microbiome transplants (VMT) from donors with healthy Lactobacillus populations led to long-term success in four out of five patients. Although promising, VMT is impractical on a large scale, making direct Lactobacillus supplementation a more feasible option [5]. These in vitro and in vivo studies demonstrate the ability of Lactobacillus to outcompete G. vaginalis overgrowth and reestablish eubiosis in the vaginal microbiome after BV biofilm formation.

H₂O₂-Producing Lactobacillus 

The most protective and resistant strains of Lactobacillus, including L. crispatus, L. jensenii, and L. gasseri, produce hydrogen peroxide (H₂O₂) as a metabolite [10,11]. The production of H₂O₂ is a predictor for long term colonization of Lactobacillus in the vagina [8]. Colonization by H₂O₂-producing Lactobacillus is associated with lower UTI, BV occurrence, and decreased inflammation [6,7,8,9]. In addition, studies suggest that Lactobacillus has a multifactorial effect by suppressing growth of other indigenous organisms and pathogens, anti-inflammatory effects, autoinhibitory effects and degradation of vaginal mucosa [10]. Some believe this is because H₂O₂ kills G. vaginalis, Candida, and other urogenital pathogens, but studies show conflicting results when testing the mechanism of H₂O₂ action [7,10,11]. For example, in one study there was no correlation between the amount of H₂O₂ produced and pathogenic bacteria inhibited [8]. This implies that the H₂O₂ is not directly responsible for the antibacterial activity of the vaginal epithelial cells, although the H₂O₂-producing Lactobacillus still promotes the antibacterial properties more than non-H₂O₂ producing Lactobacillus (L. iners). Other studies have noted that H₂O₂-producing species exclusively produce the D-isomer of lactic acid [11]. It is possible that it is not the H₂O₂ metabolite that is responsible for the inhibition of bacteria and fungi, but the Lactobacillus’ D-Lactic Acid production [11]. In another study, it was confirmed that the primary risk factor of experiencing BV was lack of H₂O₂-producing Lactobacillus (risk was four times greater) [9,10,11]. Additionally, microbiomes that were colonized by H₂O₂ Lactobacillus were the most likely to stay colonized by Lactobacillus during the study period [10]. Although the exact function of the H₂O₂ metabolite is unclear, the role of H₂O₂-producing Lactobacillus in promoting vaginal health has been demonstrated in numerous studies [7,8,9,10,11]. One strain of L. crispatus has been studied extensively as a model probiotic for the application of these mechanisms. Overall, many studies suggest that Lactobacillus has a multifactorial effect in promoting the growth of beneficial bacteria while suppressing overgrowth of indigenous harmful organisms and pathogens via autoinhibitory effects and epithelial cell adhesion. 

Lactobacillus crispatus (LACTIN-V) as a Model Probiotic for BV Recurrence 

LACTIN-V, a probiotic containing  Lactobacillus crispatus CTV-05, is currently undergoing clinical trials as a probiotic to support women with recurrent BV. One study investigated LACTIN-V supplementation to decrease incidence of BV recurrence. In this study, 12 and 24 weeks after the initial LACTIN-V dose, participants experienced recurrence significantly less (15%) than the placebo group [12]. In a similar study, LACTIN-V led to a sustained increase in L. crispatus and decrease in BV-associated organisms [13]. In both of these studies, there were no adverse events linked to the LACTIN-V supplementation [12,13]. 

Further studies of LACTIN-V specifically investigate the colonization of L. crispatus [3,14,15]. In one study,  72% of participants were colonized successfully and 28% were resistant to colonization [14]. It was discovered that the participants that were resistant to colonization had more biodiversity at initial inoculation than those that were successfully colonized [14]. This is supported by another study which found that increased diversity in the vaginal microbiome is correlated with metronidazole (antibiotic) treatment failure and BV recurrence [3]. Another trial of LACTIN-V has also noted significantly reduced odds of colonization of L. crispatus with vaginal intercourse after supplementation [15]. This suggests that while LACTIN-V shows great promise, understanding and addressing factors influencing colonization resistance will be critical for optimizing its efficacy as a therapeutic option.

Many of the previously discussed trials were phase 2 trials for LACTIN-V, aiming to prove its efficacy in women with recurrent BV. At this time, LACTIN-V is not approved by the FDA for the public, but the authors are trying to develop it under an “Investigational New Drug” application as an adjuvant therapy for recurrent BV [16]. LACTIN-V was initially used as a probiotic because it was a H₂O₂-producing strain, suggesting it would be beneficial for recurrent BV. Through these studies, there was proof of concept, as LACTIN-V was shown to significantly decrease BV recurrence and increase L. crispatus colonization to reestablish eubiosis. [13,14,16]. Given that LACTIN-V is natural, safe and effective, similar probiotics should be seriously considered as an adjuvant therapy to medications in the treatment of BV incidence.

Conclusion 

The treatment of recurrent bacterial vaginosis (BV) has traditionally relied on the use of non-selective antibiotics that often fail to provide long term relief, as they disrupt the vaginal microbiome and lead to further complications like yeast infections and BV (dysbiosis). The evidence supporting Lactobacillus, particularly H₂O₂-producing strains such as Lactobacillus crispatus, as a supplemental therapy is compelling. In both in vitro and in vivo studies, Lactobacillus has demonstrated a capacity to inhibit pathogenic bacteria like G. vaginalis, reestablish eubiosis, and reduce the recurrence of BV. Lactin-V, a specific strain of L. crispatus (CTV-05), has shown great promise in clinical trials as an effective probiotic that can be used alongside antibiotics to promote vaginal health. Although there are some limitations regarding colonization resistance in individuals with high microbiome diversity, the overall outcomes indicate that Lactobacillus supplementation, particularly strains like Lactin-V, could serve as an essential adjuvant therapy for women with recurrent BV with low risk. Future research should continue to explore the mechanisms of action behind the beneficial effects of H₂O₂-producing Lactobacillus and how to increase the rate of successful colonization. Additionally, with the amount of new research on these mechanisms and strains of H₂O₂ producing Lactobacillus, physicians treating those with recurrent BV should consider recommending this probiotic supplementally to the medications they prescribe.

About the Author: Kiley Cleland

I’m Kiley Cleland and I’m a pre-med student majoring in Biochemistry and Molecular Biology and minoring in Philosophy. I worked as a Medical Assistant for 3 years prior to transferring to UC Davis and then became a physically disabled patient. I am extremely passionate about bioethics, patient advocacy, disability rights, advocating for underserved communities and raising the standard of care in healthcare today. I have a special interest in Interventional Radiology and mentoring fellow pre-meds here at UC Davis. 

Author's Note

I wrote this review for healthcare providers and patients that are faced with Recurrent Bacterial Vaginosis (BV). I chose this topic because I dealt with it personally for years and when I went to my gynecologists, they were not able to give me treatments that had long lasting relief. I ended up doing a lot of personal research into the vaginal microbiome because I had worked in a mass spectrometry lab that studied microbiomes. In addition, Recurrent BV is misunderstood by many physicians and patients, which often only leads to more recurrence of BV instead of long term treatments. The goal of this literature review is to give a general background on what is going on in the vaginal microbiome, the reasons why recurrent BV happens, and share safe, supplemental options available today to replenish the vaginal microbiome flora that are not well known.

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