Bacterial Vaginosis as a Mixed Infection

Our understanding of bacterial vaginosis (BV) is improving through observational studies and study of the interactions between bacteria in the laboratory. The vaginal ecosystem is subjected to a variety of hormonal changes that affect the balance between lactobacilli and anaerobes. It is likely that the normal lactobacillus flora may be overwhelmed by factors such as a prolonged alteration in the pH of the vagina following vaginal douching or frequent sexual intercourse. Instillation of large numbers of organisms from a male or female sex partner might trigger BV. Alternative hypotheses include the introduction of a lytic bacteriophage infection, reducing the lactobacillus population. Once the BV organisms are allowed to flourish, they utilize each other’s metabolites in a symbiotic manner and continue to maintain a pH of >4.5. Possibly, the lack of H2O2-producing lactobacilli in the vagina makes it easier for sexually transmitted pathogens, including human immunodeficiency virus (HIV), to gain a foothold, although it may be that the same risk factors for acquiring sexually transmitted diseases (STDs) are in fact precipitating BV. There is an urgent need to determine how to effectively prevent the adverse outcomes of pregnancy associated with BV. If we could control BV, we might additionally be able to reduce the risk of HIV infection, for which BV is an important risk factor. A promising approach is to recolonize the vagina with lactobacilli that are high-level H2O2 producers and may be better able to inhibit the growth of anaerobes than the native lactobacillus flora.