The serine protease HtrA regulates Group B Streptococcus virulence and affects the host response to infection.

Group B Streptococcus (GBS) rectovaginally colonizes up to 20% of women worldwide and is a leading cause of invasive infections during pregnancy, contributing annually to a significant proportion of preterm births, neonatal infections, and stillbirths. Despite its reputation as a perinatal pathogen, GBS infection rates in non-pregnant adults are also increasing. While much progress has been made to understand transcriptional regulation of virulence by two-component systems, many aspects of GBS virulence regulation remain understudied. Although many bacterial pathogens utilize high temperature response A (HtrA) family serine proteases to regulate virulence and stress responses through varied mechanisms, the function of HtrA in GBS was unknown. Here, we demonstrate that HtrA is localized to the GBS membrane and regulates the abundance of endogenous surface and secreted proteins, including a subset of virulence factors. Although deletion of htrA (ΔhtrA) increased dissemination to placentas and fetuses, this strain caused significantly fewer adverse pregnancy outcomes compared to isogenic wild-type (WT). Placentas from ΔhtrA-infected dams contained more chemokines, pro-inflammatory IL-1β, and neutrophil myeloperoxidase than isogenic WT-infected placentas, suggesting that ΔhtrA GBS induces potent neutrophil chemotaxis. However, immunosuppressive IL-10 was present at increased concentration, which may in part explain the attenuation of adverse pregnancy outcomes during ΔhtrA infection. Finally, we note that recombinant GBS HtrA directly cleaves human fibronectin in vitro, highlighting that this protease may also target host substrates during infection. Together, these findings support a role for HtrA as a post-translational regulator of GBS virulence and suggest that inhibiting HtrA activity may hold therapeutic promise against GBS induced adverse pregnancy outcomes.