RESUMO
Staphylococcus 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 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. bNOS also promoted resistance to the pharmaceutical antibiotics that act on the cell envelope such as vancomycin and daptomycin. Surprisingly, bNOS-deficient strains gained resistance to aminoglycosides, suggesting that 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.
Assuntos
Proteínas de Bactérias/metabolismo , Resistência a Meticilina , Staphylococcus aureus Resistente à Meticilina/enzimologia , Staphylococcus aureus Resistente à Meticilina/patogenicidade , Óxido Nítrico Sintase/metabolismo , Infecções Cutâneas Estafilocócicas/enzimologia , Abscesso/genética , Abscesso/microbiologia , Abscesso/patologia , Animais , Antibacterianos/farmacologia , Peptídeos Catiônicos Antimicrobianos/farmacologia , Proteínas de Bactérias/genética , Daptomicina/farmacologia , Humanos , Staphylococcus aureus Resistente à Meticilina/genética , Camundongos , Mutação , Óxido Nítrico/metabolismo , Óxido Nítrico Sintase/genética , Espécies Reativas de Oxigênio/metabolismo , Infecções Cutâneas Estafilocócicas/genética , Infecções Cutâneas Estafilocócicas/microbiologia , Infecções Cutâneas Estafilocócicas/patologia , Vancomicina/farmacologia , CatelicidinasRESUMO
Streptococcal collagen-like protein 1 (Scl-1) is one of the most highly expressed proteins in the invasive M1T1 serotype group A Streptococcus (GAS), a globally disseminated clone associated with higher risk of severe invasive infections. Previous studies using recombinant Scl-1 protein suggested a role in cell attachment and binding and inhibition of serum proteins. Here, we studied the contribution of Scl-1 to the virulence of the M1T1 clone in the physiological context of the live bacterium by generating an isogenic strain lacking the scl-1 gene. Upon subcutaneous infection in mice, wild-type bacteria induced larger lesions than the Δscl mutant. However, loss of Scl-1 did not alter bacterial adherence to or invasion of skin keratinocytes. We found instead that Scl-1 plays a critical role in GAS resistance to human and murine phagocytic cells, allowing the bacteria to persist at the site of infection. Phenotypic analyses demonstrated that Scl-1 mediates bacterial survival in neutrophil extracellular traps (NETs) and protects GAS from antimicrobial peptides found within the NETs. Additionally, Scl-1 interferes with myeloperoxidase (MPO) release, a prerequisite for NET production, thereby suppressing NET formation. We conclude that Scl-1 is a virulence determinant in the M1T1 GAS clone, allowing GAS to subvert innate immune functions that are critical in clearing bacterial infections.