Bacterial vaginosis: when the equilibrium of the microbiota is destabilized

A few days before the development of this bacterial infection, the composition of the vaginal flora is thought to change: lactobacilli, which maintain its equilibrium, disappear gradually in favor of pathogenic bacteria initially present in the vaginal flora.

 

Bacterial vaginosis is a common vaginal infection associated with a risk of premature childbirth,  pelvic inflammatory disease and a higher risk of transmission of pathogens (including HIV). It manifests as foul-smelling vaginal discharge and itching. Women who smoke, practice vaginal douching or have an IUD are more likely to be affected by this disorder. It is also likely to be more prevalent among women who are homosexual, natives of Africa or at risk of sexually transmitted infections (STI).

Modification of vaginal pH

This infection appears when the equilibrium of the vaginal microbiota is disrupted. Depletion of lactobacilli, the bacteria responsible for maintaining a protective acidic environment, is said to promote proliferation of pathogenic bacteria naturally present in the vagina. Nevertheless, scientists do not know how this bacterial infection arises in the vaginal mucosa. To uncover the cascade of events that precedes its appearance, American researchers studied the vaginal flora of around thirty African-American women from every possible angle. The subjects were between 18 and 45 years old, and had had at least one same-sex relationship during the previous 12 months. These volunteers took samples from their vagina every day for three months.  Almost half of them developed vaginosis.

Vaginal microbiota was unbalanced before the infection

The analysis revealed that the flora of most of the women who did not contract vaginosis was dominated by Lactobacillus crispatus (a type of lactobacillus). This bacterium was present at low levels in the women who developed the infection, and other predominating lactobacillus strains struggled to maintain the equilibrium of the vaginal microbiota. Even in the absence of infection, these women displayed low but detectable levels of the bacteria suspected of causing the vaginosis in their microbiota. They would therefore be more vulnerable to infections because of an unbalanced microbiota. The study also showed that the protective lactobacilli disappeared gradually two weeks before the appearance of the infection, while there was a proliferation of pathogenic bacteria three to four days beforehand.

 

Sources:

Muzny CA, Blanchard E, Taylor CM, Aaron KJ, Talluri R, Griswold ME, Redden DT, Luo M, Welsh DA, Van Der Pol WJ, Lefkowitz EJ, Martin DH, Schwebke JR. Identification of Key Bacteria Involved in the Induction of Incident Bacterial Vaginosis: A Prospective Study. J Infect Dis. 2018 Apr 28