New research at Washington University School of Medicine in St. Louis points to a common species of bacteria as an important contributor to bacterial vaginosis (BV), a microbial imbalance of the vaginal flora. The study suggests that Gardnerella vaginalis, which is one of the most frequently isolated bacterial species in BV, may contribute to the origin of BV as well as the associated complications.

One in three women in the US have bacterial vaginosis.

Women with BV are at increased risk of sexually transmitted infections including HIV, serious pregnancy complications such as intrauterine infection and preterm birth, pelvic inflammatory disease, and infections following surgery or other routine gynecologic procedures.

In the past, researchers have frequently dismissed Gardnerella vaginalis as a potential cause of BV, because it also presents in a significant proportion of healthy women. Unlike most common infectious diseases, BV appears to be polymicrobial in nature. In fact, BV has been shown by recent genomic studies to be more complex than originally thought; not only can BV vary in bacterial composition from day to day but also from one individual to another.

More common than yeast infections, bacterial vaginosis often can be asymptomatic or cause insignificant symptoms, such as "thinning" of vaginal fluid secretions and increased pH, leaving many women unaware they have it. From the patient perspective, BV symptoms fall within the 'normal' spectrum.

"Bacterial vaginosis ... is not a common topic of conversation between patients and their gynecologists," says Amanda Lewis, PhD, assistant professor of molecular microbiology.

The condition is diagnosed through examination of the vagina and tests of the vaginal fluids. Doctors typically treat it with antibiotics, but the condition often recurs.

"Our findings, which come from new experimental models of the condition, may be a first step toward a better understanding of how to treat bacterial vaginosis and prevent serious complications linked with the condition," says Lewis. She and her colleagues worked with mice throughout the study. This is the first time vaginal infection by a BV associated bacterium in an animal has been shown to parallel the human disease with regard to clinical diagnostic features.

Nicole Gilbert, PhD, postdoctoral fellow, showed that G. vaginalis causes increased shedding of the outermost cells covering the vaginal lining. "We think the vaginal lining is shed as part of the body's effort to eliminate bacteria," says Gilbert. "However, this shedding may also expose sensitive underlying tissues. This may be important for understanding why women with bacterial vaginosis are more susceptible to sexually transmitted diseases and urinary tract infections."