New findings about vaginal bacterial flora

Abstract

The aim of this review is to update knowledge about the vaginal ecosystem, non-cultivation methods for bacterial identification (gene amplification), the Lactobacillus species that comprise normal vaginal flora and influence of host genetics on bacterial interactions with local innate and acquired immune defenses. A Medline (Pubmed) search from 1997-2009 for relevant articles was performed and the most informative articles were selected. Non-culture techniques (gene amplification) allow a comprehensive analysis of the vaginal ecosystem's composition. In the majority of women in the reproductive age there is a predominance of one or more species of Lactobacillus: L. crispatus, L. inners and L gasseri. However, in other apparently healthy women there is a deficiency or complete absence of Lactobacilli. Instead, there is a substitution by other lactic acid-producing bacteria: Atobium, Megasphaera and/or Leptotrichia species. The infectivity and/or proliferation of pathogenic bacteria in the vagina is suppressed by lactic acid production, by products of endogenous bacteria and by activation of local innate and acquired immunity. Vaginal epithelial cells produce several compounds with anti-microbial activity. These cells have Toll-like receptors on their membrane that recognize molecular patterns associated with pathogens. Recognition leads to production of pro-inflammatory cytokines and stimulation of antigen-specific immunity. The production of IgG and IgA antibodies is also triggered in the endocervix and vagina in response to infection. Vaginal flora composition and the immune mechanisms constitute important defenses. Criteria of normal and abnormal flora have to be reviewed and genetic polymorphism can explain variations in flora composition. This new knowledge should be included in the clinical practice of gynecologists and obstetricians to improve patients care.