WASHINGTON — Creating new HIV prevention tools for women has proven slow and researchers have found another hurdle: bacteria in the reproductive tract.

A new study published Thursday examined what stalled an attempt at an anti-HIV gel, and found certain types of vaginal bacteria broke down the protective medication before it worked.

The finding is the latest to link our health to the microbes that share our bodies, what’s called the microbiome. And while it highlights another difficulty in developing vaginal ‘‘microbicides’’ to block HIV infection, it offers the prospect of one day identifying women who are more vulnerable.

The research re-examined an early vaginal gel containing the AIDS drug tenofovir that had seemed partially protective in one study only to fail in another. Scientists thought maybe some women didn’t use the gel properly.

Samples saved from 688 South African women who tested that gel tell a different tale.

Some of those women had a reproductive tract dominated by species of ‘‘friendly’’ bacteria from the Lactobacillus family. Others harbored less healthy species that lead to bacterial vaginosis, inflammation that can increase risk of certain health problems.

The tenofovir gel reduced HIV infection by 61 percent in women who harbored the mostly healthy lactobacilli — but by only 18 percent in women with the less healthy vaginal bacteria, researchers reported in the journal Science.

Associated Press