Abstract
Modification of the host lipidome via secreted enzymes is an integral, but often overlooked aspect of bacterial pathogenesis. In the current era of prevalent antibiotic resistance, knowledge regarding critical host pathogen lipid interactions has the potential for use in developing novel antibacterial agents. While most studies to date on this matter have focused on specific lipids, or select lipid classes, this provides an incomplete picture. Modern methods of untargeted lipidomics have the capacity to overcome these gaps in knowledge and provide a comprehensive understanding of the role of lipid metabolism in the pathogenesis of infections. In an attempt to determine the role of lipid modifying enzymes produced by staphylococci, we exposed bovine heart lipids, a standardized model for the mammalian lipidome, to spent medium from staphylococcal cultures, and analyzed lipid molecular changes by MS/MSALL shotgun lipidomics. We elucidate distinct effects of different staphylococcal isolates, including 4 clinical isolates of the pathogenic species Staphylococcus aureus, a clinical isolate of the normally commensal species S. epidermidis, and the non-pathogenic species S. carnosus. Two highly virulent strains of S. aureus had a more profound effect on mammalian lipids and modified more lipid classes than the other staphylococcal strains. Our studies demonstrate the utility of the applied untargeted lipidomics methodology to profile lipid changes induced by different bacterial secretomes. Finally, we demonstrate the promise of this lipidomics approach in assessing the specificity of bacterial enzymes for mammalian lipid classes. Our data suggests that there may be a correlation between the bacterial expression of lipid-modifying enzymes and virulence, and could facilitate the guided discovery of lipid pathways required for bacterial infections caused by S. aureus and thereby provide insights into the generation of novel antibacterial agents.
Highlights
Infections caused by S. aureus range from skin and soft tissue infections[1], bloodstream infections[2] and infective endocarditis[3]
Three assays used to investigate lipase activity in the spent media from staphylococcal cultures are illustrated in (Fig 1). It summarizes the analytical workflow for the shotgun lipidomics approach and statistical approach to arrive at the results
Activity recorded by measuring absorbance at 412nm indicated the presence of lipase activity in spent media from S. aureus JE2 and MN8, less activity associated with Newman, and little or no detectable lipase activity in spent media from the other strains [53] (Fig 2B)
Summary
Infections caused by S. aureus range from skin and soft tissue infections[1], bloodstream infections[2] and infective endocarditis[3]. The genetic heterogeneity, diversity of virulence factors, and increasing resistance of S. aureus to antibiotics has garnered the interest of researchers for many decades. In addition to differences in the presence or absence of virulence genes, differences in the activity of several key regulators including the accessory gene regulator (Agr) [5,6] and the SaeRS two component system[7,8] can affect the S. aureus secretome. The Agr system, which regulates virulence factor production by quorum sensing, regulates the production of extracellular toxins like alpha-, beta-, delta- hemolysin, lipase and proteases. Studies aimed at determining the extracellular protein composition in agr mutants of S. aureus show that agr mutants had an increased retention of extracellular proteins in the cytosol [9] and reduced extracellular protease activity
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