Staphylococcus hominis bacteriocins protect against skin pathogens

About This Grant

PROJECT SUMMARY The surface of the skin is persistently colonized with a community of bacteria that includes numerous different species and strains of coagulase negative staphylococci (CoNS). There is mounting evidence that these CoNS prevent colonization by pathogens such Staphylococcus aureus, and protect the skin from damage induced by this pathogen. Our central hypothesis is the innovative concept that human skin S. hominis make diverse bacteriocins to limit S. aureus-induced damage to the host. In support of this hypothesis, we have discovered that several skin S. hominis isolates make bacteriocins that kill S. aureus and limit skin damage in mouse models of infection. Our preliminary findings demonstrate that one of these bacteriocins is a novel daptide antibiotic (Shom_D1) that targets S. aureus membranes, and we have also identified resistance determinants for this new bacteriocin. To better understand these mechanisms and their significance to human skin protection, in Aim 1 we will identify additional S. hominis strains that produce protective bacteriocins. We discovered multiple new bacteriocins in preliminary screens, including Shom_D1 and a uniquely potent lantibiotic (Shom_L4). We will genome sequence and bioinformatically identify additional genetic loci encoding potential bacteriocins, and we will determine the breadth of skin commensal and pathogen killing activity of these identified bacteriocins. For selected molecules we will perform structure elucidation using mass spectrometry and NMR. In Aim 2, we will define S. hominis bacteriocin killing and resistance mechanisms. Since Shom_D1 is the first daptide antibiotic discovered in Staphylococci, we will focus on determining its mechanism of action and characterizing resistance determinants, and then extend into studies on Shom_L4. We will perform membrane permeability and lipid bilayer assays with purified bacteriocins vrs controls. Finally we will explore mechanisms of resistance and distribution of resistance determinants. In Aim 3, we will determine the ability of S. hominis bacteriocins to protect skin from S. aureus damage. Our preliminary studies indicate that Shom_D1 can protect the skin from S. aureus- induced inflammation and skin damage using a mouse epicutaneous model. We hypothesize that Shom_D1 and Shom_L4 will improve skin health through prevention of pathogen-induced inflammation and improve wound healing. We will test the purified Shom_D1 and Shom_L4, or we will use S. hominis bacteriocin producing strains, in competition with S. aureus in a mouse epicutaneous model and a wound model. We will also perform single cell and spatial RNA sequencing to determine host responses when S. aureus is challenged with Shom_D1 and Shom_L4 in a mouse wound model. Collectively, the findings from the proposed work will shed light on the mechanisms used by the commensal skin CoNS community to fight pathogens and protect the host.