MRSA bNOS affects antibiotic sensitivity and abscess formation 1 Methicillin-Resistant Staphylococcus aureus Bacterial Nitric Oxide Synthase Affects Antibiotic Sensitivity and Skin Abscess Development

Staphylococcus aureus (S. aureus) infections present an enormous global health concern complicated by an alarming increase in antibiotic resistance. S. aureus is among the few bacterial species that express nitric oxide synthase (bNOS), and thus can catalyze nitric oxide (NO) production from L-arginine. Here we generate an isogenic bNOS-deficient mutant in the epidemic community-acquired methicillin-resistant S. aureus (MRSA) USA300 clone to study its contribution to virulence and antibiotic susceptibility. Loss of bNOS increased MRSA susceptibility to reactive oxygen species and host cathelicidin antimicrobial peptides, which correlated with increased MRSA killing by human neutrophils and within neutrophil extracellular traps (NETs). bNOS also promoted resistance to the pharmaceutical antibiotics that act on the cell enveloppe such as vancomycin and daptomycin. Correspondingly, bNOS activity was increased upon vancomycin exposure. Surprisingly, bNOS-deficient strains gained resistance to aminoglycosides, suggesting the role of bNOS in antibiotic susceptibility is more complex than previously observed in Bacillus species. Finally, the MRSA bNOS mutant showed reduced virulence with decreased survival and smaller abscess generation in a mouse subcutaneous infection model. Together these data indicate that bNOS contributes to MRSA innate immune and antibiotic resistance phenotypes. Future development of specific bNOS inhibitors could be an attractive option to simultaneously reduce MRSA pathology and enhance its susceptibility to commonly used antibiotics. http://www.jbc.org/cgi/doi/10.1074/jbc.M112.448738 The latest version is at JBC Papers in Press. Published on January 15, 2013 as Manuscript M112.448738