The human body is commonly assisted by a number of friendly bacteria that live within it, but the exact types of bacteria and the means by which they help is not always understood. A research team at the University of North Carolina at Chapel Hill may have found one breed of bacteria in vaginal mucus that can help protect women from HIV and other sexually transmitted diseases.
Mucosal surfaces such as those in the lungs, intestinal tract, and vagina are a form of initial defense against invaders. The mucus linings are secreted regularly, carrying away anything trapped within. This is true of vagina mucus as well, which is important in stopping invaders from reaching the cells of the vaginal wall. It is best imagined as a form of biological condom. However, the effectiveness of this barrier is not consistent from woman to woman and can even vary within the same individual. The research team wanted to know why.
For the study, HIV “pseudovirus” particles were used. These are particles that can spread in a manner similar to HIV, but are harmless to the body. Thirty-one women of reproductive age were introduced to the pseudovirus and vaginal mucus samples were taken. The samples were examined under high-powered microscopy to assess whether the pseudovirus particles spread freely or became trapped in the mucus.
The bacteria the study eventually focused on is called lactobacillus crispatus, and it lives in vaginal mucus. As it is a moist, open area, the vagina is known to have its own microbiota—a microscopic ecology. The vagina’s environment is considered healthy when it is dominated by any of the lactobacillus species. However, it is crispatus specifically that has been found to help protect against HIV.
Among the samples taken from the participating women, two general groups became apparent. One group of mucus was effective at trapping HIV particles, and one was not. Interestingly, the efficacy of trapping was not correlated to the mucus’s pH value, total lactic acid, or the ratio of lactobacillus bacteria compared to other microbes (called a Nugent score). The most noticeable difference was that the “trapping” groups had much higher levels of D-lactic acid. Humans do not produce D-lactic acid—it’s secreted by bacteria when they digest food and is sometimes used as an indicator of infection. Some gene sequencing followed to find the source of the acid, and the result was lactobacillus crispatus.
While the dominance of other lactobacillus bacteria resulted in a “tighter” mesh of mucus, it was the increased “stickiness” that crispatus triggered that improved the protection against HIV and other STDs. More research will determine the exact level of benefit a crispatus-dominated vagina provides, along with possible treatment options to increase crispatus levels in women. This discovery is especially relevant to women in Africa, as past research has noted that African women generally have vaginal environments dominated by non-crispatus bacteria.
The findings were published in MBio, the online journal of the American Society for Microbiology.
Sources for Today’s Article:
Nunn, K., et al., “Enhanced Trapping of HIV-1 by Human Cervicovaginal Mucus Is Associated with Lactobacillus Crispatus-Dominant Microbiota,” MBio 2015; doi:10.1128/mBio.01084-15.
Smith, S.M., et al., “Use of D-Lactic Acid Measurements in the Diagnosis of Bacterial Infections,” Journal of Infectious Diseases 2015; 27(3): 658–64.
“UNC-Chapel Hill Researchers Reveal Type of Vaginal Bacteria That Protects Women from HIV,” EurekAlert! web site, October 8, 2015; http://www.eurekalert.org/pub_releases/2015-10/uonc-uhr100815.php.
“Vaginal Microbes Influence Whether Mucus Can Trap HIV Virus,” ASM Society, October 6, 2015; http://www.asm.org/index.php/journal-press-releases/93810-vaginal-microbes-influence-whether-mucus-can-trap-hiv-virus.