Background: Fluoroquinolones are broad-spectrum antibiotics widely used in the treatment of bacterial infections such as Staphylococcus aureus isolates. Resistance to these antibiotics is increasing.
Material/Methods: The occurrence of mutations in the grlA and gyrA loci were evaluated in 69 fluoroquinolone-resistant S. aureus isolates from 2 teaching hospitals of Tehran University of Medical Sciences.
Results: Out of the 165 S. aureus isolates, 87 (52.7%) were resistant to methicillin and 69 (41.8%) were resistant to fluoroquinolone. Fluoroquinolone-resistant S. aureus isolates had a mutation at codon 80 in the grlA gene and different mutational combinations in the gyrA gene. These mutational combinations included 45 isolates at codons 84 and 86, 23 isolates at codons 84, 86 and 106 and 1 isolate at codons 84, 86 and 90. Fluoroquinolone-resistant S. aureus isolates were clustered into 33 PFGE types.
Conclusions: The findings of this study show that the fluoroquinolone-resistant S. aureus strains isolated in the teaching hospitals in Tehran had multiple mutations in the QRDRs region of both grlA and gyrA genes.

Keywords: Microbial Sensitivity Tests, Mutation - genetics, Iran, Genotype, Genes, Bacterial - genetics, Fluoroquinolones - pharmacology, Electrophoresis, Gel, Pulsed-Field, Drug Resistance, Bacterial - genetics, Phenotype, Staphylococcus aureus - isolation & purification