The effect of oral Metronidazole on the vaginal microbiome of patients with recurrent bacterial vaginosis: A pilot investigational study

Bacterial vaginosis (BV) is the most common vaginal problem in reproductive-age women. Recurrent BV, defined as having at least three BV episodes in one year, causes significant psychological distress and can prove challenging to resolve. Using 16S rRNA sequencing, we characterized the vaginal microbiome of 63 women aged 18–40 years. We compared the vaginal microbiome of 17 patients presenting with an acute episode of recurrent BV to 46 healthy controls. The effect of oral Metronidazole treatment on the vaginal microbiome of the recurrent BV patients was analyzed 7–10 days and 30–40 days after the completed the standard 7-day oral twice-a-day Metronidazole treatment regimen. Beta diversity (unweighted UniFrac distances) of recurrent BV patients’ vaginal microbiome differed significantly from healthy controls (p = 0.01). Compared to controls, Mycoplasma, Veillonella, and Sneathia genera were more dominant in the recurrent BV cohort, while Lactobacilleacae was less abundant. After one week of oral Metronidazole treatment, recurrent BV patients’ vaginal microbiome was significantly altered [alpha diversity, p = 0.005; beta diversity, p = 0.03], and there was an increase in healthy commensals such as Lactobacillaceae. However, these changes were not sustained one month after treatment. Our findings show that the vaginal microbiome of recurrent BV patients differs from healthy controls, and that Metronidazole as monotherapy may be insufficient treatment for recurrent BV, as it only alters the vaginal microbiome temporarily. Future investigations into alternative therapies that restore a healthy vaginal microbiome are necessary.