Painter Kimberley L, Strange Elizabeth, Parkhill Julian, Bamford Kathleen B, Armstrong-James Darius, Edwards Andrew M
MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom.
Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom.
Infect Immun. 2015 May;83(5):1830-44. doi: 10.1128/IAI.03016-14. Epub 2015 Feb 17.
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.
慢性复发性金黄色葡萄球菌感染的发展与被称为小菌落变体（SCV）的生长缓慢突变体的出现有关，这些突变体对抗生素具有高度耐受性，并且能够在宿主细胞内存活。然而，在感染过程中支撑SCV出现的宿主和细菌因素却知之甚少。在此，我们证明，将金黄色葡萄球菌暴露于亚致死浓度的H2O2会导致庆大霉素抗性SCV的群体频率出现特定的、剂量依赖性增加。时间进程分析表明，H2O2暴露在野生型细胞中引起抑菌作用，在此期间SCV在金黄色葡萄球菌群体中自发出现。这是通过一种诱变DNA修复途径发生的，该途径包括DNA双链断裂修复蛋白RexAB、重组酶A和聚合酶V。除了通过提高突变率触发SCV出现外，H2O2还选择了SCV表型，导致表型稳定性增加，并通过降低SCV回复为野生型的速率进一步增加了SCV亚群的大小。随后的分析表明，SCV对H2O2的毒性作用比野生型细菌具有显著更高的抗性。除了血红素营养缺陷型外，庆大霉素抗性SCV比野生型细菌表现出更高的过氧化氢酶活性，这有助于它们对H2O2的抗性。综上所述，这些数据揭示了一种机制，通过该机制金黄色葡萄球菌通过产生具有增强过氧化氢酶产生的H2O2抗性SCV亚群来适应氧化应激。
