SUN-198 Vaginal Microbial Diversity Changes across the Menstrual Cycle in Healthy Young Women

The vaginal microbiome, the collection of microorganisms and their metabolites residing in the vaginal tract, is critical for maintaining women’s health. For example, the vaginal microbiome protects against pathogens by maintaining a low-pH environment. In particular, Lactobacillus species predominate most vaginal microbiomes and produce lactic acid, which has been cited as a key protector of vaginal health. Meanwhile, disruptions to the finely balanced vaginal microbiome can cause infections, such as bacterial vaginosis, and may contribute to the development of endometrial and ovarian cancer. While the crucial and diverse role of the vaginal microbiome is becoming more apparent, very little is known about the endogenous factors that influence its composition and stability. Cell culture and qPCR studies suggest that reduced estradiol levels decrease Lactobacillus species colonization, but the effects on other species are unknown. In the present study, we tested the hypothesis that the vaginal microbiota composition changes over the menstrual cycle. Volunteer participants from a women’s college self-swabbed vaginal samples daily for 2 months, while recording timing of menstruation and contraceptive use with a mobile application. High-throughput 16S rRNA sequencing was done to identify the microbial compositions of each sample. The high temporal resolution of this study allows the capture of time-dependent effects otherwise lacking in previous cohort studies. As measured by the Shannon index, the majority (5 out of 8) of participants who were not using hormonal contraception had higher alpha diversity during menstruation (p < 0.05), suggesting that fluctuations in hormones during menstruation alter vaginal microbiota composition. In contrast, only 1 out of 6 participants using oral contraceptives had higher vaginal microbial diversity during menstruation (p < 0.001), suggesting oral contraceptives decrease diversity at menstruation. We are currently analyzing which microbes contribute to these differences in diversity. In addition, we are analyzing these vaginal microbiota data for effects of diet, exercise and mood. Our goal is to establish a foundation for understanding how hormones interact with other factors to influence the vaginal microbiome. These findings could provide long-term, time-longitudinal insights into how the vaginal microbiome is involved in reproductive tract cancers in women.