A fungal pathobiont promotes Streptococcus agalactiae vaginal persistence and pathogenesis through physical and metabolic interactions.

Complex polymicrobial interactions at the host interface can shape the mucosal landscape and tip the scales between commensalism and pathogenicity. Here, we use a newly adapted murine model of vaginal colonization to show that the human pathobiont Candida albicans (Ca) supports Group B Streptococcus (GBS) fitness in the vaginal tract and ascension to the uterus. GBS frequently colonizes the vagina asymptomatically; however, during pregnancy, colonization can lead to adverse outcomes and neonatal invasive infection. Using human vaginal isolates of Ca and GBS, we demonstrate that physical interactions contribute to persistence. Triple RNA sequencing of Ca, GBS, and a physiologically relevant model of the human vaginal epithelium reveals that GBS induces arginine biosynthesis in Ca. This drives the expression of bacterial virulence factors and primes GBS for adhesion to the epithelium. We show that interkingdom nutrient exchange can increase GBS pathogenic potential and identify a new target for preventative therapies.