Vaginal flora in health and disease.

This chapter has portrayed the normal vaginal flora as a range of microbial species that associates in a stable way with human vaginal epithelium. The human vagina provides these microorganisms with the physical and chemical environment that allows them to use this tissue as a normal habitat. Because the relationship of the normal flora to the underlying tissue is that of an ecosystem, the components of this system are in dynamic equilibrium. Consequently, a change in the environmental conditions provided by the vaginal epithelium will result in changes in the population density or the species composition of the normal flora. Although the microbial flora appears to provide a benefit to the host by reducing the probability of colonization by exogenous microorganisms, it may participate in various undesirable symptoms, including various types of vaginitis or postoperative, postabortion, and post-Caesarean section infections, and upper tract invasion after lower tract infection. All future attempts to understand vaginitis in all its manifestations necessarily must include recognition of the importance of the normal flora because all types of vaginitis are superimposed on an existing endogenous microbial flora.