Determinants of polymicrobial diabetic wound infections

PROJECT SUMMARY Group B Streptococcus (GBS), is an opportunistic pathogen that asymptomatically colonizes the urogenital and female reproductive tract of approximately 25-30% of individuals. However, GBS can cause serious infections in immunocompromised individuals including those with diabetes. Diabetic wound infections are a major public

health burden, with approximately 25% of diabetic individuals developing a wound in their lifetime, 25% of these wounds not healing and 28% requiring surgical amputation. Poor infection outcomes are correlated with the presence of numerous bacterial pathogens, and GBS, along with Staphylococcus aureus, is one of the most

common bacteria found in these wounds. Despite its prevalence, no prior work has been done on GBS pathogenesis in the diabetic wound environment. Recently, we developed a Type 2 diabetic murine model of GBS diabetic wound infection in leprdb mice, and demonstrated that GBS forms a robust wound and persists in

this environment. Further observations found that GBS colonies recovered from diabetic wound tissue were hyper-pigmented/hemolytic, suggesting selection of more virulent GBS mutants during diabetic infection. These phenotypes mimic those of a covR mutant, as CovR is a major repressor of GBS virulence factors such

as the GBS hemolysin/pigment, nuclease (NucA), and surface adhesin plasminogen binding protein PbsP. Dual RNA-sequencing of GBS and the murine wound revealed that these same CovR regulated genes were highly upregulated in the diabetic wound. In addition, GBS infection triggered the recruitment of neutrophils, neutrophil

activation and NET formation at the site of infection. Finally, we have shown in our murine model that the presence of S. aureus promotes GBS persistence in the diabetic wound. With these preliminary data, we have formulated hypotheses which address multiple mechanisms by which GBS may survive and persist in the

diabetic wound environment. These hypotheses will be addressed in the following specific aims: Aim 1: Determine how CovR regulation contributes to diabetic wound infection, Aim 2: Characterize the contribution of PbsP to GBS diabetic wound formation, persistence, and dissemination, Aim 3: Examine the contribution of nuclease activity in promoting GBS immune evasion and wound persistence. These

studies will increase our understanding of the pathogenesis of GBS diabetic wound infection and will provide a platform for additional studies.