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US Team Characterizes Vaginal Microbes in Women from Different Ethnic Backgrounds

By a GenomeWeb staff reporter

NEW YORK (GenomeWeb News) – The microbial communities associated with the vagina vary from one woman to the next and between women from different ethnic backgrounds, according to a microbiome study appearing online this week in the Proceedings of the National Academy of Sciences.

Using 16S rRNA pyrosequencing and other approaches, researchers from the Universities of Maryland and Idaho, Emory University, and Proctor and Gamble assessed microbe communities and pH levels in vaginal samples from nearly 400 healthy North American women, identifying differences in both microbial community profiles and salinity within and between women from the four ethnic groups tested.

In the process, the team also pinned down five characteristic vaginal microbial community types — some containing microbes best known for their role in disease.

"Even microbes that were previously believed to be detrimental to a woman's health seem to be part of a normal ecosystem in some women, according to this study," lead author Jacques Ravel, a microbiology and immunology researcher with the University of Maryland's Institute for Genome Sciences, said in a statement.

Past research suggests Lactobacillus bacteria and other lactic acid-producing bugs may help protect against bacterial and yeast infections, sexually transmitted infections, and other vaginal ailments by keeping the vaginal environment slightly acidic, Ravel and his co-workers explained. Nevertheless, they added, relatively few studies have been done using methods that allow the characterization of both cultureable and uncultureable microbes across large numbers of women.

To explore the "microbial ecosystem" of the vagina in more detail, the researchers recruited 396 North American women between the ages of 12 and 45 years old at clinics in Baltimore and Atlanta. Participants were of Caucasian, African-American, Hispanic, or Asian descent, with equal numbers of individuals from each ethnic group.

Using the Roche 454 FLX platform, the team sequenced the V1-V2 hyper-variable 16S rRNA regions from genomic DNA isolated from self-collected vaginal swabs. As part of the study, a clinical nurse measured vaginal pH for each individual. Vaginal samples were also tested for bacterial vaginosis.

When the researchers began sorting through the sequences found in the vaginal samples, they identified 282 taxa in the women sampled.

Rather than finding a single core vaginal microbiome, the researchers explained, they identified five main community groups — four containing an over-representation of the Lactobacillus species L. iners, L. crispatus, L. gasseri, and L. jensenii, and a fifth group with far fewer lactic acid bacteria and more strictly anaerobic microbes such as bacteria in the Aerococcus, Finegoldia, and Prevotella genera.

But the relative abundance of each community and vaginal pH both differed significantly among the women tested, apparently correlating in part with ethnicity. For instance, almost 90 percent of Caucasian women and about 80 percent of Asian women carried Lactobacillus-dominated communities, compared with about 60 percent of Hispanic women and 62 percent of African-American women.

Consistent with these patterns, Hispanic and African-American women tended to have decreased vaginal acidity compared to Asian and Caucasian women, based on median pH measurements.

"Further research is needed to establish the function of these microbes and the communities in which they appear," Ravel said. "Some of the seemingly beneficial microbial communities seem to be associated with a higher pH — a measure of acidity — which is usually considered to be unhealthy."

Given their findings so far, the researchers argue that it might be time to re-think what constitutes a normal healthy vaginal microbiome. And, they say, disease risk and diagnoses may need to be tailored to account for individual microbiome differences as well as ethnicity-related differences.

"We've found we can actually group women by the type of microbes they have in the vagina," Ravel said in a statement. "We may not need to personalize reproductive medicine down to the individual woman, but by which microbial group they belong to."

Moreover, he added, it may eventually be possible to harness vaginal microbial information to identify individuals at increased risk of infections such as bacterial vaginosis or for guiding some treatments.