Multiple mutations conferring ciprofloxacin resistance in Staphylococcus aureus demonstrate long-term stability in an antibiotic-free environment

J Antimicrob Chemother. 2000 Mar;45(3):353-6. doi: 10.1093/jac/45.3.353.


Two unrelated strains of Staphylococcus aureus, one with a single mutation in grlA, the other with multiple mutations in gyrA, gyrB, grlA, grlB, norA and the norA promoter region, encoding low-level and high-level ciprofloxacin resistance, respectively, were studied. The characterized mutations in these genes were conserved when both strains were passaged for at least 500 generations in an antibiotic-free environment. New, rapidly stabilized mutations and higher MICs were detected for strains passaged in sub-MIC ciprofloxacin concentrations. The seeming irreversibility of quinolone resistance may affect the long-term success of this drug class.

MeSH terms

  • Anti-Infective Agents / pharmacology*
  • Ciprofloxacin / pharmacology*
  • Drug Resistance, Microbial
  • Genotype
  • Microbial Sensitivity Tests
  • Mutation / genetics*
  • Phenotype
  • Point Mutation / genetics
  • Point Mutation / physiology
  • Promoter Regions, Genetic / genetics
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / genetics*


  • Anti-Infective Agents
  • Ciprofloxacin