The microbiota normally associated with the human body have an important influence on human development, physiology, immunity and nutrition. The vast majority of these indigenous microbiota exist in a mutualistic relationship with their human host, while others are opportunistic pathogens that can cause both chronic infections and life-threatening diseases.
Much of our research has focused on determining the kinds of bacterial communities present in vaginas of asymptomatic healthy women. These communities play a critical role in maintaining health by creating a low pH environment that is inhospitable to non-indigenous organisms.
We seek to ascertain their functions and identify factors that influence community composition and dynamics. Using cultivation-independent methods, we have analyzed the species composition and structure of vaginal communities found in nearly 400 healthy women of four ethnic groups in North America. The results showed there were five community state types that profoundly differed in terms of species composition; however, in all cases they were dominated by lactic acid producing bacteria indicating that all communities performed in a similar way. More recently we characterized the temporal dynamics of vaginal bacterial communities. The analysis revealed the dynamics of five major classes of bacterial communities and showed that some communities change markedly over short time periods, whereas others were relatively stable. The women studied were healthy; thus, it appears that neither variation in community composition per se nor higher levels of observed diversity (co-dominance) are necessarily indicative of dysbiosis. However, we do postulate that intervals of increased susceptibility to disease may occur because the vaginal microbiota vary over time.
The drivers of change in vaginal communities are unknown, but the key to understanding these community dynamics may rest in unraveling the mutualistic relationship that exists between vaginal bacterial communities and the host. The bacteria in the vagina rely entirely upon the host for substrates they require for growth, thus the quantity and kinds of substrates available may directly govern community composition. Additionally, species of Lactobacillus are known to require exogenous sources of various amino acids, vitamins and cofactors. In the vagina, the host and other bacterial populations must meet these requirements. This leads us to postulate that defining nutritional networks may be key to understanding stable community performance. Elucidating these networks and gaining insight to the roles of innate and adaptive immune systems may provide the information needed to develop strategies for management of these ecosystems in ways that reduce risk to disease.