Effect of metronidazole on vaginal microbiota associated with asymptomatic bacterial vaginosis

Interpretation of vaginal metagenomic characteristics in different types of vaginitis

Although vaginitis is closely related to vaginal microecology in females, the precise composition and functional potential of different types of vaginitis remain unclear. Here, metagenomic sequencing was applied to analyze the vaginal flora in patients with various forms of vaginitis, including cases with a clue cell proportion ranging from 1% to 20% (Clue1_20), bacterial vaginitis (BV), vulvovaginal candidiasis (VVC), and BV combined with VVC (VVC_BV). Our results identified Prevotella as an important biomarker between BV and Clue1_20. Moreover, a gradual decrease was observed in the relative abundance of shikimic acid metabolism associated with bacteria producing indole as well as a decline in the abundance of Gardnerella vaginalis in patients with BV, Clue1_20, and healthy women. Interestingly, the vaginal flora of patients in the VVC_BV group exhibited structural similarities to that of the VVC group, and its potentially functional characteristics resembled those of the BV and VVC groups. Finally, Lactobacillus crispatus was found in high abundance in healthy samples, greatly contributing to the stability of the vaginal environment. For the further study of L. crispatus, we isolated five strains of L. crispatus from healthy samples and evaluated their capacity to inhibit G. vaginalis biofilms and produce lactic acid in vitro to select the potential probiotic candidate for improving vaginitis in future clinical studies. Overall, we successfully identified bacterial biomarkers of different vaginitis and characterized the dynamic shifts in vaginal flora between patients with BV and healthy females. This research advances our understanding and holds great promise in enhancing clinical approaches for the treatment of vaginitis.

IMPORTANCE

Vaginitis is one of the most common gynecological diseases, mostly caused by infections of pathogens such as Candida albicans and Gardnerella vaginalis. In recent years, it has been found that the stability of the vaginal flora plays an important role in vaginitis. Furthermore, the abundant Lactobacillus-producing rich lactic acid in the vagina provides a healthy acidic environment such as Lactobacillus crispatus. The metabolites of Lactobacillus can inhibit the colonization of pathogens. Here, we collected the vaginal samples of patients with bacterial vaginitis (BV), vulvovaginal candidiasis (VVC), and BV combined with VVC to discover the differences and relationships among the different kinds of vaginitis by metagenomic sequencing. Furthermore, because of the importance of L. crispatus in promoting vaginal health, we isolated multiple strains from vaginal samples of healthy females and chose the most promising strain with potential probiotic benefits to provide clinical implications for treatment strategies.

Orally administrated Lactobacillus gasseri TM13 and Lactobacillus crispatus LG55 can restore the vaginal health of patients recovering from bacterial vaginosis

Bacterial vaginosis (BV) is a common infection of the lower genital tract with a vaginal microbiome dysbiosis caused by decreasing of lactobacilli. Previous studies suggested that supplementation with live Lactobacillus may benefit the recovery of BV, however, the outcomes vary in people from different regions. Herein, we aim to evaluate the effectiveness of oral Chinese-origin Lactobacillus with adjuvant metronidazole (MET) on treating Chinese BV patients. In total, 67 Chinese women with BV were enrolled in this parallel controlled trial and randomly assigned to two study groups: a control group treated with MET vaginal suppositories for 7 days and a probiotic group treated with oral Lactobacillus gasseri TM13 and Lactobacillus crispatus LG55 as an adjuvant to MET for 30 days. By comparing the participants with Nugent Scores ≥ 7 and < 7 on days 14, 30, and 90, we found that oral administration of probiotics did not improve BV cure rates (72.73% and 84.00% at day 14, 57.14% and 60.00% at day 30, 32.14% and 48.39% at day 90 for probiotic and control group respectively). However, the probiotics were effective in restoring vaginal health after cure by showing higher proportion of participants with Nugent Scores < 4 in the probiotic group compared to the control group (87.50% and 71.43% on day 14, 93.75% and 88.89% on day 30, and 77.78% and 66.67% on day 90). The relative abundance of the probiotic strains was significantly increased in the intestinal microbiome of the probiotic group compared to the control group at day 14, but no significance was detected after 30 and 90 days. Also, the probiotics were not detected in vaginal microbiome, suggesting that L. gasseri TM13 and L. crispatus LG55 mainly acted through the intestine. A higher abundance of Prevotella timonensis at baseline was significantly associated with long-term cure failure of BV and greatly contributed to the enrichment of the lipid IVA synthesis pathway, which could aggravate inflammation response. To sum up, L. gasseri TM13 and L. crispatus LG55 can restore the vaginal health of patients recovering from BV, and individualized intervention mode should be developed to restore the vaginal health of patients recovering from BV.

Clinical trial registration

https://classic.clinicaltrials.gov/ct2/show/, identifier NCT04771728.

Natural progress history of asymptomatic bacterial vaginosis in Chinese Han women and associated risk factors

OBJECTIVE

Asymptomatic bacterial vaginosis (aBV) is prevalent in the general population, while a previous study only investigated the natural history of aBV in women at high-risk. This stage study was to investigate the natural history of aBV in Chinese Han women at general risk and examine risk factors associated with different outcomes.

METHODS

Women of reproductive age with aBV were enrolled and prospectively followed up with for four months. Participants were classified into one of three outcomes: progress, self-cure or no-change. Univariate and multivariate analyses were used to determine the association between potential risk factors and outcomes.

RESULTS

A total of 3420 subjects were screened and 1014 women with aBV were enrolled. Eventually, 984 participants completed the study, with 30 patients dropped out. Among the 984 cases, 42 cases self-cured spontaneously, while 433 cases progressed and 509 cases did not change significantly. Of the 433 cases that progressed, several types of mixed infections were observed in addition to 196 symptomatic bacterial vaginosis. According to univariate analysis, frequent travel (OR, 95% CI, 2.73 [2.09 ~ 3.55]) and history of bacterial vaginosis (BV) (5.47, [4.15 ~ 7.21]) exhibited significant associations with aBV progression, while condom contraception (0.46 [0.36 ~ 0.61]) and lower Nugent score (0.49, [0.37 ~ 0.64]) demonstrated protective effects for self-cure. According to multivariate regression analysis, the risk factors for aBV progression were history of BV (6.67, [4.86 ~ 9.15]) and frequent travel (3.57, 2.59 ~ 4.92). Condom contraception (0.36, 0.26 ~ 0.49) exhibited a protective effect against aBV progression.

CONCLUSION

Without intervention, a large proportion of aBV would progress, compared to the very few patients whose aBV self-cured spontaneously. It is necessary to clinically intervene aBV patients. Condom utilization can be used as an effective method to improve the outcome of aBV.

Association of key species of vaginal bacteria of recurrent bacterial vaginosis patients before and after oral metronidazole therapy with short- and long-term clinical outcomes

Bacterial vaginosis (BV) is associated with a state of vaginal dysbiosis typically involving depletion of otherwise dominant populations of Lactobacillus. The causes of this microbial succession are not known; there may be multiple causes. Standard treatment includes oral metronidazole, which typically restores Lactobacillus species to dominance. However, recurrence rates are high; recurrent BV patients recur 3–4 times annually and are often refractory to treatment. Our previous qPCR-based study of recurrent BV patients pointed to putatively more virulent species of Gardnerella that were associated with refractory responses to oral metronidazole, and less robust recovery of Lactobacillus species associated with recurrence after an initial period of remission. However, these associations did not account for outcomes in all patients, suggesting that other bacterial species were involved. In this follow-up study, we sequenced the V4 domain of 16S rRNA sequences of 41of these same patients pre- and posttreatment. Overall compositions among pretreatment clinical outcome groups were not different, although alpha diversity significantly decreased: refractory > recurrent > remission. Combinations of key species were associated with and prognostic for outcome. Higher pretreatment abundance of Megasphaera lornae together with lower abundance of Gardnerella Gsp07 and Finegoldia magna predicted long term remission after oral metronidazole. Furthermore, a subset of refractory patients that did not have high levels of Gardnerella Gsp07, instead had elevated levels of alternative species including Atopobium vaginae, Mageeibacillus indolicus (BVAB3), and Prevotella timonensis. Patients who recurred after transient remission had elevated abundance of species including Atopobium vaginae, Gardnerella, and Aerococcus christensenii, compared to long-term remission patients. Core bacterial species among refractory patients did not change in abundance after metronidazole, suggesting resistance or tolerance, in contrast to the loss in abundance of the same species among recurrent or remission patients. These findings have potential prognostic and therapeutic implications.

The Role of Antimicrobial Resistance in Refractory and Recurrent Bacterial Vaginosis and Current Recommendations for Treatment

Bacterial vaginosis (BV), the most common cause of vaginal discharge, is characterized by a shift in the vaginal microbiota from Lactobacillus species dominance to a diverse array of facultative and strict anaerobic bacteria which form a multi-species biofilm on vaginal epithelial cells. The rate of BV recurrence after therapy is high, often >60%. The BV biofilm itself likely contributes to recurrent and refractory disease after treatment by reducing antimicrobial penetration. However, antimicrobial resistance in BV-associated bacteria, including those both within the biofilm and the vaginal canal, may be the result of independent, unrelated bacterial properties. In the absence of new, more potent antimicrobial agents to eradicate drug-resistant pathogenic vaginal microbiota, treatment advances in refractory and recurrent BV have employed new strategies incorporating combination therapy. Such strategies include the use of combination antimicrobial regimens as well as alternative approaches such as probiotics and vaginal fluid transfer. Our current recommendations for the treatment of refractory and recurrent BV are provided.