Inhibition of Staphylococcus aureus virulence by Corynebacterium secreted factors

About This Grant

Project Summary This proposal addresses the protective function of the airway microbiome against infection with the major bacterial pathogen Staphylococcus aureus. In the upper airway, the abundance of non-pathogenic Corynebacterium correlates with reduced colonization and infection with S. aureus and other pathogens. Further, longitudinal studies indicate that Corynebacterium abundance is predictive of infection risk, with a greater abundance of Corynebacterium associated with reduced risk of infection. However, the mechanisms by which Corynebacterium may contribute to infection defense remain largely unclear. In recent work published in Infection and Immunity, we found that pre-exposure to Corynebacterium results in improved clearance of S. aureus from the lungs in a mouse infection model. This enhanced protection correlated with reduced S. aureus adherence to human respiratory tract epithelial cells in vitro. We also discovered that Corynebacterium cell-free conditioned media (CFCM) was sufficient to block the activity of S. aureus hemolysins, a key virulence feature of this pathogen. Preliminary data suggest a secreted protease in Corynebacterium CFCM is responsible for hemolysin inhibition. Using size exclusion chromatography, we identified a specific fraction of the CFCM containing the hemolysin blocking activity. For this proposal, we aim to identify and characterize the putative Corynebacterium protease responsible for blocking S. aureus hemolysis. Hemolysins are a type of pore forming toxin in S. aureus which can lyse several host cell types including red blood cells, epithelial cells, and neutrophils, a critical innate immune cell that contributes to S. aureus clearance by bacterial killing. Our overall hypothesis is that a Corynebacterium secreted protease improves protection against S. aureus infection by cleaving pore forming toxins, resulting in reduced S. aureus cytotoxicity in epithelial cells and neutrophils. To address this hypothesis, Aim 1 will focus on the identification and characterization of the Corynebacterium protease. Our preliminary data indicate that Corynebacterium CFCM blocks hemolysis of red blood cells caused by alpha-hemolysin (Hla). The known properties of Hla hemolysis will be used to interrogate the steps which are impaired by Corynebacterium activity, including binding to the receptor ADAM10 and pore formation. Aim 2 interrogates the effect of Corynebacterium CFCM on epithelial cells and neutrophils as two key host cells mediating defense against S. aureus infection. Together, these studies will advance our understanding of how Corynebacterium contribute to protection against S. aureus by abrogating S. aureus pore forming toxin activity and characterize a novel factor responsible for Corynebacterium-mediated interference with S. aureus virulence activities.