Bacterial vaginosis (BV), a common gynecologic syndrome characterized by a Lactobacillus-deficient vaginal microbiome, is linked to significant reproductive health outcomes such as spontaneous preterm birth, cervical dysplasia, and sexually transmitted infection (STI) acquisition. Standard of care treatment with metronidazole (MTZ) may provide immediate symptomatic relief but frequently results in rapid recurrence, partially due to its propensity to promote dominance by recurrence-associated Lactobacillus iners instead of optimal health-associated Lactobacillus crispatus. Rapid antibiotic resistance development by BV-associated bacteria, such as Gardnerella species, may also contribute to treatment failure. Previously, our group demonstrated that oleic acid, an unsaturated long-chain fatty acid (LCFA), simultaneously inhibits L. iners and certain BV-associated bacteria, including MTZ-resistant Gardnerella, while promoting the growth of L. crispatus, establishing the potential therapeutic role of this metabolite class.
We systematically screened a broad panel of related LCFAs on L. iners and BV-associated bacterial isolates from the U.S. and South Africa, revealing 10(R)-hydroxystearic acid (10(R)-HSA), a metabolic derivative of oleic acid, as a top candidate with therapeutically-relevant cross-strain microbial potency. We covalently conjugated 10(R)-HSA with MTZ to create MTZ-10(R)HSA, a molecule which retains the independent activities of each component. Treatment of BV-like mock communities with MTZ-10(R)HSA as well as coadministration of MTZ and 10(R)HSA outperformed MTZ alone in promoting L. crispatus dominance, emphasizing the importance of a multi-targeting approach. Additionally, we found that both combination therapies hinder antibiotic resistance development in Gardnerella vaginalis compared to MTZ alone, with next-generation sequencing revealing that selective pressure from 10(R)-HSA induced mutational changes in several key bacterial metabolic pathways. These results highlight that this dual-pronged approach to BV treatment may improve upon the current standard of care, helping to alleviate the global clinical burden of BV.