This protocol is a prospective, interventional, randomized, double-blind, placebo controlled longitudinal study designed to investigate the microbiomic and immunologic perturbations that lead to vulvovaginal candidiasis (VVC) in women who receive antibiotics. VVC is the most common fungal infection affecting women. Although asymptomatic vaginal Candida colonization occurs in ~10-20% of healthy women, ~75% of women will experience at least one episode of symptomatic VVC during their lifetime. Nonetheless, the local mucosal factors that allow Candida to convert from a commensal organism to an opportunistic pathogen are not well defined. Antibiotic use (particularly beta-lactams) is a well-recognized risk factor for the development of VVC in healthy women, suggesting that alterations in the endogenous vaginal microbial flora results in deregulation of local mucosal anti-Candida immune responses. However, which commensal vaginal microbiota are important for protection against Candida infection, and the mechanism(s) whereby vaginal microbiota influence the local mucosal immune response against Candida, remain unknown.