# Effect of Metronidazole on Concentrations of Vaginal Bacteria Associated with Risk of HIV Acquisition

## TL;DR

Metronidazole reduces harmful vaginal bacteria linked to higher HIV risk, but some bacteria take longer to eliminate.

## Contribution

This study quantifies metronidazole's effect on 13 BV-associated bacterial taxa and identifies variable clearance times.

## Key findings

- Metronidazole reduced bacterial DNA concentrations by 2.3–4.5 log10-fold across all taxa.
- Some bacteria like Gemella asaccharolytica required over 7 days for suppression.
- Bacterial concentrations often dropped below qPCR detection limits, suggesting eradication.

## Abstract

Several bacterial vaginosis (BV)-associated bacteria have been associated with elevated risk of HIV acquisition, however susceptibility of these bacteria to antibiotics is poorly understood. Vaginal samples were collected from 22 persons daily for two weeks following BV diagnosis. Metronidazole treatment was prescribed for 5–7 days. Changes in bacterial concentrations were measured with taxon-specific 16S rRNA gene quantitative PCR (qPCR) assays. A culture-based antimicrobial assay confirmed presence of antibiotics in vaginal swab samples. Bacterial DNA concentrations decreased during antibiotic administration for all thirteen bacterial taxa tested. Comparison of bacterial DNA concentrations in samples before administration of antibiotics to samples taken on the last day of antimicrobial assay-confirmed antibiotic presence showed a 2.3–4.5 log10-fold decrease across all taxa. Concentrations were frequently reduced to the qPCR assay’s limit of detection, suggesting eradication of bacteria. Mean clearance time varied across taxa (1.2–8.6 days), with several bacteria (e.g., Gemella asaccharolytica, Sneathia spp., Eggerthella-like sp.) taking >7 days to suppress. Metronidazole reduces quantities of bacterial taxa associated with increased HIV acquisition risk. Eradication of high-risk vaginal bacteria using metronidazole is one promising avenue for reducing HIV acquisition risk. A 5–7-day treatment course may not be sufficient to suppress all bacteria.

Metronidazole significantly decreases concentrations of numerous vaginal bacteria associated with increased HIV infection risk. The time course of bacterial eradication was variable and depended on initial bacterial concentrations. Metronidazole treatment offers one potential avenue to decrease HIV infection risk.