Rapid method for detection of gyrA and grlA mutations in unrelated strains of Staphylococci susceptible and resistant to levofloxacin

New Microbiol. 2001 Oct;24(4):347-53.


A panel of 150 clinical isolates of methicillin resistant and susceptible Staphylococci were investigated using a rapid and simple PCR-RFLPs technique to detect DNA nucleotide changes at the site of the most frequently reported mutations in grlA (codons 79, 80) and gyrA (codons 83, 84) genes which confer fluorquinolone resistance in Staphylococci. Convergent dual mutations in and gyrA and grlA were found in all strains exhibiting resistance to ciprofloxacin (MIC, 8 to > or =128 mg/l) and levofloxacin (MIC, 8 to > or =64 mg/l). Mutations in grlA and gyrA were also found in strains susceptible to levofloxacin and resistant to ciprofloxacin. In our sample no strains with only grlA mutations were found. Our data indicate that methicillin-resistant fluorquinolone-resistant strains are likely to have mutations in both grlA and gyrA. In contrast, methicillin-susceptible strains do not show any mutation. The genetic relatedness of a sample of representative epidemiologically unrelated MRSA strains, tested by PFGE and rep-PCR, are in agreement with the hypothesis of a clonal selection of these resistant strains.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Infective Agents / pharmacology*
  • DNA Gyrase / genetics*
  • DNA Topoisomerase IV / genetics
  • Genetic Testing
  • Genotype
  • Levofloxacin*
  • Methicillin Resistance
  • Mutation
  • Ofloxacin / pharmacology*
  • Polymerase Chain Reaction
  • Polymorphism, Restriction Fragment Length
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / genetics*


  • Anti-Infective Agents
  • Levofloxacin
  • Ofloxacin
  • DNA Topoisomerase IV
  • DNA Gyrase