Ravel and his co-authors collected vaginal bacterial samples from 32 healthy, reproductive-age women twice a week for four months, and then analyzed the samples using genomic techniques.
Again the researchers found five basic bacterial communities, and also noted that some changed rapidly in the same woman while others stayed stable.
In some cases, the collection of bacteria seen in a particular woman would have indicated the presence of bacterial vaginosis, although these women were healthy and not experiencing any symptoms.
"This changes what we consider to be a normal bacterial community in the vagina," Dewhurst said.
Changes in bacterial communities tended to correspond with estrogen levels at different points in the menstrual cycle, the particular composition of bacteria in a woman's vagina and sexual activity.
It's also likely that what a woman eats or the environment in which she lives will affect microbial composition, Ravel added.
The authors postulated that microbiota that fluctuated regularly may make a woman more vulnerable to infection.
"Bacterial vaginosis is linked to transmission of HIV and other sexually transmitted diseases, so this is a potentially significant risk factor for acquiring sexually transmitted diseases," Dewhurst said.
And if it turns out that there is a "new normal" of vaginal microbiota depending on the woman, this could curb the overuse of antibiotics, the authors said.
Vaginal bacteria also can affect pregnancy and fertility. The composition of vaginal microbiota and of a man's sperm could mean that a woman is fertile with one man and infertile with another, an accompanying editorial suggested.
"We need to rethink the way we approach women's health and treatment and diagnosis," Ravel said.
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