Temporal Dynamics of the Human Vaginal Microbiota

The vaginal microbiome is dynamic, varying over time in composition and function with implications for women’s health. What’s Up with Vaginal Microbes? The ability to properly identify women at risk of acquiring sexually transmitted infectious diseases or who might suffer from adverse obstetric sequelae is a critical first step in reducing their incidence and the unnecessary use of antibiotics. Currently, patients undergo a clinical examination of the vagina that includes measuring the pH and evaluating the amount and type of discharge and the presence of odor. These criteria are thought to be surrogates for the presence of an “abnormal” vaginal microbiota. Although these kinds of tests, done only once, could be used to diagnose conditions such as bacterial vaginosis, it is debatable whether they are accurate predictors of risk because little is known about how the composition and function of the vaginal microbiome changes over time. Previous studies have established that in healthy asymptomatic women, five types of vaginal microbiota exist that differ in the kinds of microbes they contain. It was thought that each type carries its own risks and particular response to environmental disturbances, such as sexual activity or hygiene practices. In an exciting new study, Gajer and colleagues now describe changes in the identity and abundance of bacteria in the vaginal communities of 32 women by analyzing vaginal samples obtained twice weekly over a 16-week period. The kinds of bacteria present in the samples were identified by classifying thousands of 16S rRNA gene sequences in each sample using high-throughput next-generation sequencing. The authors further characterized vaginal community function by determining the metabolites produced throughout the 16-week period. Gajer and colleagues found that there were five longitudinal patterns of change in vaginal microbial community composition. Moreover, in some women, the vaginal microbial community composition changed markedly and rapidly over time, whereas in others it was relatively stable. Using statistical modeling, the authors showed that the menstrual cycle influenced the stability of the vaginal communities. In many cases, the metabolite profiles indicated that vaginal community function was maintained despite changes in bacterial composition. Intervals of increased susceptibility to disease may occur because the vaginal microbiota varies over time. The authors envision that better knowledge of the causes and consequences of these changes to the host will lead to the development of new strategies to manage vaginal microbiomes in ways that promote health and minimize the use of antibiotics. Elucidating the factors that impinge on the stability of bacterial communities in the vagina may help in predicting the risk of diseases that affect women’s health. Here, we describe the temporal dynamics of the composition of vaginal bacterial communities in 32 reproductive-age women over a 16-week period. 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 are relatively stable. Modeling community stability using new quantitative measures indicates that deviation from stability correlates with time in the menstrual cycle, bacterial community composition, and sexual activity. The women studied are 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.