Mutations in the gyrA and grlA genes of quinolone-resistant clinical isolates of methicillin-resistant Staphylococcus aureus

J Antimicrob Chemother. 1996 Sep;38(3):543-6. doi: 10.1093/jac/38.3.543.


The mutations in the quinolone-resistance determining regions (QRDR) of the gyrA, gyrB and grlA genes and in the norA gene from five clinical isolates of methicillin resistant Staphylococcus aureus (MRSA) were examined by DNA sequencing. The mutation from Ser84 to Leu in GyrA was associated with relatively high-level resistance to quinolones, whereas the mutation from Glu88 to Gly or Lys in GyrA was associated with low-level resistance to quinolones. Mutations of the grlA gene were observed at codon 80 (Ser80) or 84 (Glu84), independent of the mutations of gyrA. No mutations were observed in either the gyrB or norA genes.

MeSH terms

  • Anti-Infective Agents / pharmacology*
  • Bacterial Proteins / drug effects
  • Bacterial Proteins / genetics
  • DNA Gyrase
  • DNA Topoisomerase IV
  • DNA Topoisomerases, Type II / drug effects
  • DNA Topoisomerases, Type II / genetics*
  • Fluoroquinolones
  • Methicillin Resistance / genetics*
  • Microbial Sensitivity Tests
  • Multidrug Resistance-Associated Proteins
  • Mutation*
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / genetics


  • Anti-Infective Agents
  • Bacterial Proteins
  • Fluoroquinolones
  • Multidrug Resistance-Associated Proteins
  • NorA protein, Staphylococcus
  • DNA Topoisomerase IV
  • DNA Gyrase
  • DNA Topoisomerases, Type II