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

A panel of 150 clinical isolates of methicillin resistant and susceptible S taphylococci were investigated using a rapid and simple PCR-RFLPs technique to detect DNA nucleotide changes at the site of the most frequently report ed mutations in grlA (codons 79, 80) and gyrA (codons 83, 84) genes which c onfer fluorquinolone resistance in Staphylococci. Convergent dual mutations in and gyrA and grlA were found in all strains exhibiting resistance to ci profloxacin (MIC, 8 to greater than or equal to 128 mg/l) and levofloxacin (MIC, 8 to greater than or equal to 64 mg/l). Mutations in grlA and gyrA we re also found in strains susceptible to levofloxacin and resistant to cipro floxacin. 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, methicilli n-susceptible strains do not show any mutation. The genetic relatedness of a sample of representative epidemiologically unrelated MRSA strains, tested by PFGE arid rep-PCR, are in agreement with the hypothesis of a clonal sel ection of these resistant strains.