Vaginal bacteria could actually protect women from HIV

The microbiota found within female reproductive mucus could help protect women from sexually transmitted diseases including HIV, researchers from the University of North Carolina reported in the latest edition of the open-access journal mBio.
Sam Lai, senior author of the study and an assistant professor at the UNC Eshelman School of Pharmacy, and his colleagues found that some women had a stronger, or at least more effective, natural barrier against the virus that causes AIDS and other types of STDs.
As the UNC team explained in a statement, vaginal microbiota is considered to be healthy if it is dominated by any species of lactobacillus. Now they’ve discovered that one specific type of this bacteria, lactobacillus crispatus, appears to play a key role in sustaining the mucus barrier against HIV. The discovery, Lai said, could lead to new ways to protect women from the virus.
“What we discovered is that a woman’s risk of being infected by HIV can be affected by the type of helpful bacteria present in vaginal mucus,” the UNC professor explained. “We found that vaginal microorganisms, including specific species of lactobacillus bacteria, can directly alter the protective properties of cervicovaginal mucus.”
Elevated levels of D-lactic acid proved to be the key
As part of their research, Lai’s team examined mucus from more than 30 reproductive-age women. They utilized high-resolution time-lapse microscopy to investigate whether fluorescent HIV pseudovirus particles would become trapped in the mucus or move about freely.
They discovered that there were essentially two different types of mucus samples– those that trapped HIV well, and those that didn’t. Further analysis showed that the ability to trap the virus was not linked to the pH balance of the mucus, its total lactic acid content, or its Nugent score (a measurement of how much lactobacillus bacteria it contains compared to other microbes).
There was one distinct difference between the two groups, however: the group that did a better job of trapping HIV contained higher levels of D-lactic acid. Since humans are unable to produce D-lactic acid on their own, the study authors believed that bacteria living within the mucus layer may have been responsible for this difference.
As it turned out, the HIV-trapping mucus contained a great deal of lactobacillus crispatus while those that did not trap the virus were either dominated by another species, lactobacillus iners, or contained several different types of bacteria, including gardnerella vaginalis. Both latter types of bacteria are often associated with bacterial vaginosis, a disease caused by excessive vaginal bacteria.
Lai’s team is working on a way to reinforce the mucus barrier against disease-causing agents, as well as a technique to use antibodies, delivered either directly to the mucosal surfaces or through a vaccination, that is capable of immobilizing pathogens in the mucus layer, they said.
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Pictured is lactobacillus crispatus. Image credit: UNSW Embryology Wiki