Objective: To determine grlA and gyrA mutations in ciprofloxacin- methicillin-resistant Staphylococcus aureus isolates and their susceptibility to current antimicrobials, including a newer fluoroquinolone gatifloxacin, glycopeptides vancomycin, teicoplanin and oxazolidinone linezolid.
Methods: A total of 56 methicillin-resistant S. aureus (MRSA) isolates were collected during 2003-2006 from inpatients of Süleyman Demirel University Hospital. The isolates were confirmed to be MRSA by the production of coagulase, showing resistance against cefoxitin and having the mecA gene and tested by disk diffusion for susceptibility to vancomycin, teicoplanin and linezolid. The minimum inhibitory concentrations (MICs) of ciprofloxacin and gatifloxacin were measured using the E-test. The quinolone resistance determining regions (QRDRs) of isolates were amplified by PCR and mutations in grlA and gyrA genes were identified by direct sequencing.
Results: Sequencing data revealed that 96% of our isolates had mutations in both grlA and gyrA genes. Among these, the grlA mutation of Ser-80-Phe or Tyr and the gyrA mutation of Ser-84-Leu were the most dominant ones being detected in 50 (89%) and 40 (71%) isolates, respectively. Although 96% of isolates were highly resistant to ciprofloxacin (MIC, >or=32 mg/l), only 54% of ciprofloxacin-resistant MRSA isolates were resistant to gatifloxacin and exhibited lower-level resistance (MIC, <or=6 mg/l). Of the isolates tested, 46% were found to be susceptible to gatifloxacin (MIC, <or=0.5 mg/l). Full susceptibility was observed for vancomycin, teicoplanin and linezolid.
Conclusions: This study provided information on grlA and gyrA mutations and current antimicrobial susceptibility in clinical MRSA isolates. The results indicated that gatifloxacin is still effective against MRSA isolates and might be useful for treatment of less serious MRSA infections but careful monitoring of susceptibility is required.