Chlamydia trachomatis is the most common bacterial sexually transmitted infection (STI), with more than 130 million cases globally every year, and it poses serious health risks, especially for women. Now, researchers have found that certain bacteria in the vaginal microbiota are associated with an increased risk of Chlamydia infection.

The findings, published in Cell, suggest that targeted interventions based on these microbial markers could help reduce infection rates.

Key risk factors for Chlamydia infection include having multiple sexual partners, a history of STIs, and bacterial vaginosis — a condition that disrupts the vaginal microbiota. However, separating the effects of bacterial vaginosis from other risk behaviors is challenging.

To explore how the microbiota may predispose individuals to Chlamydia infection, a team of researchers led by Mykhaylo Usyk at Albert Einstein College of Medicine in New York compared the vaginal microbes of women who later developed the infection with those who did not.

Infection risk

Women with bacterial vaginosis had a 62% increased risk of Chlamydia infection than women without bacterial vaginosis, and their vaginal microbiotas showed significant differences, including a higher bacterial diversity. 

Sexual behaviors, such as having multiple sexual partners, did not influence infection risk through bacterial vaginosis. Instead, specific bacterial communities within the vaginal microbiota were linked to infection. A specific subtype of bacterial vaginosis — called mBV-A — was linked to a higher risk. 

The researchers also identified a set of 10 bacteria that are associated with increased risk of Chlamydia infection. Among these bacteria are Candidatus Lachnocurva vaginae, Prevotella and Megasphaera. 

Health risks

After treatment, women’s vaginal microbiotas recovered, but the levels of certain bacterial communities remained elevated. These included the mBV-A subtype, which was linked to reinfection and other health risks, such as pelvic inflammatory disease and miscarriage.

Although the findings are limited by small sample sizes and self-reported data, the study suggests that certain features of the vaginal microbiota, including specific bacterial communities, could indicate an increased Chlamydia infection risk.
“This understanding may form the basis of new public health measures to reduce the burden of [Chlamydia trachomatis] infections by development of preventive and therapeutic strategies based on more granular features of the [cervicovaginal microbiome],” the authors say.