title: Genetic changes associated with glycopeptide resistance in Staphylococcus aureus: predominance of amino acid substitutions in YvqF/VraSR.
abstract: OBJECTIVE
  To further understand the mechanism of intermediate-level glycopeptide resistance, resulting from multiple endogenous mutations, in both laboratory-derived and clinically isolated Staphylococcus aureus.
  
  
  METHODS
  Laboratory-derived S. aureus strains were generated under selection using a variety of cell-wall-active antibiotics. Complete sequences of 27 genes, including 17 two-component histidine kinase sensors, were then compared with those of their susceptible parent strain. Further genetic analysis was performed on 125 clinical S. aureus isolates and 42 geographically diverse isolates of vancomycin-intermediate S. aureus (VISA).
  
  
  RESULTS
  Selective pressure using imipenem resulted in single point mutations leading to amino acid substitutions in two genes: vraS, encoding a two-component histidine kinase sensor; and SA1702 (also called yvqF, located immediately upstream of vraS), encoding a conserved hypothetical protein. The accumulation of the mutation in two distinct proteins-MsrR, a peptide methionine sulphoxide reductase regulator, and TcaA, a teicoplanin-resistance-associated protein-correlated with further increases in the glycopeptide MIC. The prevalence of YvqF/VraSR mutants among 125 clinical isolates along with the corresponding teicoplanin MICs was as follows: 0% (0/39), < or =1 mg/L; 48.6% (17/35), 2 mg/L; 72.7% (24/33), 4 mg/L; 93.8% (15/16), 8 mg/L; and 100% (2/2), 16 mg/L. Genetic analysis of 42 VISA isolates also identified the predominant amino acid substitutions in YvqF/VraS: 9 isolates (21.4%) revealed mutations in YvqF, followed by 7 isolates with mutations in VraS (16.7%).
  
  
  CONCLUSIONS
  Our findings provide novel insights into the high prevalence and genetic diversity of YvqF/VraSR mutants among clinical S. aureus isolates with reduced susceptibility to teicoplanin.
authors.affiliation: Pharmaceutical Research Center, Meiji Seika Kaisha, Ltd, Kohoku-ku, Yokohama, Japan. yoshihisa_kato@meiji.co.jp
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kato
authors.forename: Takahisa
authors.initials: T
authors.lastname: Suzuki
authors.forename: Takashi
authors.initials: T
authors.lastname: Ida
authors.forename: Kazunori
authors.initials: K
authors.lastname: Maebashi
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D024881:Drug Resistance, Bacterial; D014644:Genetic Variation; D006020:Glycopeptides / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D020125:Mutation, Missense; D017354:Point Mutation; D015995:Prevalence; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D006020:Glycopeptides; C478170:VraR protein, Staphylococcus aureus; C478169:VraS protein, Staphylococcus aureus