PROJECT SUMMARY Infections during pregnancy or the neonatal period account for more than two million deaths globally each year. Frequently, the pathogens causing these infections begin as residents of the maternal vaginal microbiota and ascend to the uterus during pregnancy. One such pathogen, group B Streptococcus (GBS), is a leading agent neonatal morbidity and mortality, yet the factors driving GBS ascension into the uterus are poorly defined. The current standard of care, antibiotic prophylaxis to GBS-positive mothers, is insufficient to prevent GBS- associated preterm births of stillbirths and exposes ~1 million U.S. infants to antibiotics each year. Understanding the biological principles controlling GBS-host dynamics is critical to developing defined, long-lasting preventions for GBS infections in pregnancy and the early neonatal period. Clinical studies have identified gestational diabetes mellitus (GDM) as a key risk factor for maternal colonization and neonatal disease. The objective of this proposal is to interrogate the contribution of maternal immunity and GBS transcriptional adaptions in the propagation of GDM-associated invasive GBS disease and adverse birth outcomes. Our preliminary murine studies show enhanced susceptibility of diabetic mice to GBS fetal dissemination and adverse outcomes, altered cytokine profiles, and differential GBS gene expression in a novel murine GDM model. We hypothesize that GDM renders the host more susceptible to GBS by perturbing maternal immunity and altering GBS transcription to enhance virulence and fitness. This hypothesis will be interrogated through specific aims designed to determine: 1) the impact of GDM on the maternal and fetal immune responses at baseline and during GBS ascending infection, and 2) the transcriptional adaptions required for GBS pathogenesis in the pregnant host in the presence or absence of GDM. These aims are advanced using multiple innovative tools including recently established murine models of GDM and GBS vaginal colonization, immune profiling across maternal and fetal tissues, and comparative GBS transcriptional analyses from commensal and invasive niches. This research takes place in the dynamic and interdisciplinary environment of Baylor College of Medicine and the Texas Medical Center with diverse expertise in GBS-host interactions of the female reproductive tract, employment of animal models to study gestational diabetes mellitus, and genetics of Streptococcal pathogenesis. This research strategy seeks to more fully understand the complex processes governing host and pathogen dynamics in the context of pregnancy and maternal metabolic disease. These studies will launch mechanistic studies into key pathways dictating pregnancy outcomes, and will inform new therapeutic strategies for detecting and preventing GBS infections in both healthy women and those with gestational diabetes.