Group B Streptococcal Pathogenesis in Diabetic Wounds

Diabetic wound infections have poor healing outcomes due to the presence of numerous pathogens in addition to an impaired immune response. Group B Streptococcus (GBS) is one of the most commonly isolated bacteria from diabetic wound infections, but virulence mechanisms GBS uses during these infections have not been investigated. Here, we developed a new murine model of GBS diabetic wound infection to determine how GBS establishes infection and persists in the wound environment. Using dual RNA sequencing, we demonstrate that GBS infection of diabetic wounds triggers an inflammatory response, leading to increased transcript levels of inflammatory cytokines and chemokines as well as markers of neutrophil degranulation such as myeloperoxidase, calprotectin, and elastase. We then confirm that diabetic wounds infected with GBS have significantly higher abundance of Il-1b, KC (CXCL1), myeloperoxidase, calprotectin and elastase in wound tissues than uninfected controls . When examining how GBS adapts to this hyper-inflammatory environment we find that GBS upregulates numerous virulence factors including the surface plasminogen-binding protein pbsP, the nuclease nucA, the cyl operon which is responsible for hemolysin production and pigmentation as well as numerous effectors of type VII secretion. In addition, we recovered multiple hyper-pigmented/hemolytic GBS colonies from the murine diabetic wound environment which encode mutations in the two-component system covRS. We then go on to demonstrate that a mutant in cylE, which is repressed by CovR, is attenuated in diabetic wound infection. Finally, we examine the most highly upregulated gene pbsP in diabetic wound infection and find that PbsP is necessary for diabetic wound infection via adherence to the skin and promotion of inflammation. Overall design: We performed RNA-sequencing of Group B Streptococcus in 3 different conditions as well as mus musculus in 4 different conditions.