title: Staphylococcus aureus adapts to oxidative stress by producing H2O2-resistant small-colony variants via the SOS response.
abstract: The development of chronic and recurrent Staphylococcus aureus infections is associated with the emergence of slow-growing mutants known as small-colony variants (SCVs), which are highly tolerant of antibiotics and can survive inside host cells. However, the host and bacterial factors which underpin SCV emergence during infection are poorly understood. Here, we demonstrate that exposure of S. aureus to sublethal concentrations of H2O2 leads to a specific, dose-dependent increase in the population frequency of gentamicin-resistant SCVs. Time course analyses revealed that H2O2 exposure caused bacteriostasis in wild-type cells during which time SCVs appeared spontaneously within the S. aureus population. This occurred via a mutagenic DNA repair pathway that included DNA double-strand break repair proteins RexAB, recombinase A, and polymerase V. In addition to triggering SCV emergence by increasing the mutation rate, H2O2 also selected for the SCV phenotype, leading to increased phenotypic stability and further enhancing the size of the SCV subpopulation by reducing the rate of SCV reversion to the wild type. Subsequent analyses revealed that SCVs were significantly more resistant to the toxic effects of H2O2 than wild-type bacteria. With the exception of heme auxotrophs, gentamicin-resistant SCVs displayed greater catalase activity than wild-type bacteria, which contributed to their resistance to H2O2. Taken together, these data reveal a mechanism by which S. aureus adapts to oxidative stress via the production of a subpopulation of H2O2-resistant SCVs with enhanced catalase production.
authors.affiliation: MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom.
authors.forename: Kimberley L
authors.initials: KL
authors.lastname: Painter
authors.affiliation: MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Strange
authors.affiliation: Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom.
authors.forename: Julian
authors.identifier: http://orcid.org/0000-0002-7069-5958
authors.initials: J
authors.lastname: Parkhill
authors.affiliation: Department of Microbiology, Hammersmith Campus, Imperial College Healthcare NHS Trust, London, United Kingdom.
authors.forename: Kathleen B
authors.initials: KB
authors.lastname: Bamford
authors.affiliation: Department of Medicine, Imperial College London, London, United Kingdom.
authors.forename: Darius
authors.initials: D
authors.lastname: Armstrong-James
authors.affiliation: MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom a.edwards@imperial.ac.uk.
authors.forename: Andrew M
authors.identifier: http://orcid.org/0000-0002-7173-7355
authors.initials: AM
authors.lastname: Edwards
mesh_terms: D000220:Adaptation, Biological; D002374:Catalase / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000633:toxicity*; D018384:Oxidative Stress; D045522:Recombinases / Q000378:metabolism; D013014:SOS Response, Genetics; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development / Q000502:physiology*
chemical_list: D045522:Recombinases; D006861:Hydrogen Peroxide; D002374:Catalase; D004259:DNA-Directed DNA Polymerase