Phenotypic and Genotypic Characterization of Nosocomial Isolates of Staphylococcus aureus with Reference to Methicillin Resistance

Purpose: To investigate the occurrence, species prevalence, antibacterial resistance, and molecular characteristics of S. aureus isolates from different wards located in a university hospital. Methods: A total of one hundred and fifty S. aureus isolates were recovered from various clinical specimens. The isolates were tested phenotypically by conventional methods and genotypically by polymease chain reaction (PCR) for direct detection of femB and mecA genes. Results: Thirty one isolates (20.7 %) of these were identified as methicillin-resistant Staphylococcus aureus (MRSA) by oxacillin agar screen test and 124 (82.7 %) of the isolates were β-lactamase producers. The prevalence of MRSA strains among S. aureus isolates was 20.7 %. The overall resistance of MRSA to a variety of antibiotics tested was linezolid, 48.7 %; ciprofloxacin, 15.3 %; sulfamethoxazole/trimethoprim (TMS), 14.0 %; gentamicin, 12.7 %; and rifampicin, 6.7 %. All MRSA isolates were positive for femB and mecA genes; one MSSA carried mecA gene. Conclusion: Since S. aureus isolates are commonly associated with wound infections, skin and soft tissue infections and blood stream infections, glycopeptides, mupirocin, and quinupristin/dalfopristin (Q/D) would be the most effective antibiotics for the treatment of MRSA infections.