CHARACTERIZATION OF GYRA, GYRB, GRLA AND GRLB MUTATIONS IN FLUOROQUINOLONE-RESISTANT CLINICAL ISOLATES OF STAPHYLOCOCCUS-AUREUS

The distribution of fluoroquinolone resistance-associated point mutati ons in genes encoding the subunits of DNA gyrase and DNA topoisomerase IV was examined in 110 clinical isolates of Staphylococcus aureus. Po int mutations were detected by polymerase chain reaction (PCR) and res triction fragment length polymorphism analysis and mutations were furt her characterized by sequencing of PCR products. Mutations at Ser84 of GyrA were widely distributed among isolates exhibiting various degree s of fluoroquinolone resistance, and border zones between mutant and n on-mutant strains based on drug susceptibility were generally distinct . Mutations at Ser80 of GrlA were also widely distributed, but border zones between mutant and non-mutant isolates were in this case less di stinct and several GrlA mutants were highly susceptible to sparfloxaci n and tosufloxacin. Only two gyrB mutants and one grlB mutant were obs erved among the isolates: all contained a previously unreported mutati on. GyrA and grlA mutations thus appear to impart high levels of fluor oquinolone resistance in many S. aureus clinical isolates.