Mechanisms of quinolone resistance in clinical strains of Pseudomonas aeruginosa

Microb Drug Resist. Winter 1998;4(4):257-61. doi: 10.1089/mdr.1998.4.257.


Principal mechanisms of bacterial resistance to quinolones are modification of target enzymes, DNA gyrase (gyrA) and topoisomerase IV (parC), or reduction of intracellular concentration due to mutations in the regulatory genes for efflux systems, such as mexR and nfxB. We have examined gyrA, parC, mexR, and nfxB genes from 16 quinolone-resistant clinical isolates of Pseudomonas aeruginosa to determine the relation between mutations in DNA replicating enzymes or regulatory genes for efflux systems and to correlate the mutations with minimal inhibitory concentrations (MICs). The quinolone resistance-determining regions (QRDR) of these genes were amplified by PCR and sequenced by capillary electrophoresis. Fourteen of 16 isolates had mutations in gyrA, and 13/14 strains with MIC to norfloxacin > or = 8 mg/L had threonine at position 83 changed to isoleucine. Seven of 8 strains with MIC > or = 32 mg/L had mutations in parC. One of these strains showed a parC mutation at position 74 without any mutation in gyrA. Four strains had mexR and two strains nfxB mutations. The data indicate that gyrA mutation is the most important component of quinolone resistance, and simultaneous presence of parC mutations is associated with high-level resistance. parC mutation alone may contribute to resistance, and gyrA mutation may not be a prerequisite for parC mutation to express resistance. mexR and nfxB mutations were found mostly in strains with high-level resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Infective Agents / pharmacology*
  • Bacterial Proteins / drug effects
  • Bacterial Proteins / genetics
  • Ciprofloxacin / pharmacology
  • DNA Gyrase
  • DNA Topoisomerase IV
  • DNA Topoisomerases, Type II / drug effects
  • DNA Topoisomerases, Type II / genetics*
  • DNA-Binding Proteins / drug effects
  • DNA-Binding Proteins / genetics
  • Drug Resistance, Microbial
  • Fluoroquinolones*
  • Humans
  • Mutation
  • Naphthyridines / pharmacology
  • Norfloxacin / pharmacology
  • Pseudomonas aeruginosa / drug effects*
  • Pseudomonas aeruginosa / enzymology
  • Pseudomonas aeruginosa / genetics*
  • Pseudomonas aeruginosa / isolation & purification
  • Transcription Factors*


  • Anti-Infective Agents
  • Bacterial Proteins
  • DNA-Binding Proteins
  • Fluoroquinolones
  • Naphthyridines
  • NfxB protein, Pseudomonas aeruginosa
  • Transcription Factors
  • Ciprofloxacin
  • trovafloxacin
  • DNA Topoisomerase IV
  • DNA Gyrase
  • DNA Topoisomerases, Type II
  • Norfloxacin