Group B <i>Streptococcus cpsE</i> Is Required for Serotype V Capsule Production and Aids in Biofilm Formation and Ascending Infection of the Reproductive Tract during Pregnancy

Abstract

Group B <i>Streptococcus</i> (GBS) is an encapsulated Gram-positive pathogen that causes ascending infections of the reproductive tract during pregnancy. The capsule of this organism is a critical virulence factor that has been implicated in a variety of cellular processes to promote pathogenesis. Primarily comprised of carbohydrates, the GBS capsule and its synthesis is driven by the <u>c</u>apsule <u>p</u>olysaccharide <u>s</u>ynthesis (<i>cps</i>) operon. The <i>cpsE</i> gene within this operon encodes a putative glycosyltransferase that is responsible for the transfer of a Glc-1-P from UDP-Glc to an undecaprenyl lipid molecule. We hypothesized that the <i>cpsE</i> gene product is important for GBS virulence and ascending infection during pregnancy. Our work demonstrates that a GBS <i>cpsE</i> mutant secretes fewer carbohydrates, has a reduced capsule, and forms less biofilm than the wild-type parental strain. We show that, compared to the parental strain, the <i>ΔcpsE</i> deletion mutant is more readily taken up by human placental macrophages and has a significantly attenuated ability to invade and proliferate in the mouse reproductive tract. Taken together, these results demonstrate that the <i>cpsE</i> gene product is an important virulence factor that aids in GBS colonization and invasion of the gravid reproductive tract.