Staphylococcus aureus Strain Newman D2C Contains Mutations in Major Regulatory Pathways That Cripple Its Pathogenesis

Staphylococcus aureus is a major human pathogen that imposes a great burden on the health care system. In the development of antistaphylococcal modalities intended to reduce the burden of staphylococcal disease, it is imperative to select appropriate models of S. aureus strains when assessing the efficacy of novel agents. Here, using whole-genome sequencing, we reveal that the commonly used strain Newman D2C from the American Type Culture Collection (ATCC) contains mutations that render the strain essentially avirulent. Importantly, Newman D2C is often inaccurately referred to as simply "Newman" in many publications, leading investigators to believe it is the well-described pathogenic strain Newman. This study reveals that Newman D2C carries a stop mutation in the open reading frame of the virulence gene regulator, agrA In addition, Newman D2C carries a single-nucleotide polymorphism (SNP) in the global virulence regulator gene saeR that results in loss of protein function. This loss of function is highlighted by complementation studies, where the saeR allele from Newman D2C is incapable of restoring functionality to an saeR-null mutant. Additional functional assessment was achieved through the use of biochemical assays for protein secretion, ex vivo intoxications of human immune cells, and in vivo infections. Altogether, our study highlights the importance of judiciously screening for genetic changes in model S. aureus strains when assessing pathogenesis or the efficacy of novel agents. Moreover, we have identified a novel SNP in the virulence regulator gene saeR that directly affects the ability of the protein product to activate S. aureus virulence pathways.IMPORTANCEStaphylococcus aureus is a human pathogen that imposes an enormous burden on health care systems worldwide. This bacterium is capable of evoking a multitude of disease states that can range from self-limiting skin infections to life-threatening bacteremia. To combat these infections, numerous investigations are under way to develop therapeutics capable of thwarting the deadly effects of the bacterium. To generate successful treatments, it is of paramount importance that investigators use suitable models for examining the efficacy of the drugs under study. Here, we demonstrate that a strain of S. aureus commonly used for drug efficacy studies is severely mutated and displays markedly reduced pathogenicity. As such, the organism is an inappropriate model for disease studies.