مجله دانشکده پزشکی اصفهان (Mar 2012)
Comparison of the Results of Polymerase Chain Reaction and Oxacillin Agar Dilution Methods in Determining Resistance to Methicillin in Isolated Staphylococcus Aureus at Alzahra Hospital, Isfahan, Iran
Abstract
Background: Staphylococcus aureus is an important infectious bacterium. The pathogenicity of this bacterium is critical in both society and hospital. It is a human normal flora that exists in the upper respiratory tract of 25% of healthy individuals. It causes a wide spectrum of diseases ranging from skin infections to severe infections including septicemia, endocarditis, pneumonia, and skin abscess. S. aureus is a considerable factor of severe infections in both society and hospital. Methicillin resistant S. aureus (MRSA) strains have high mortality rates. Therefore, the rate of MRSA must be quickly identified and controlled with treating measures. Methods: A total number of 114 strains of S. aureus were obtained from the specimens at Alzahra Hospital, Isfahan, Iran. Minimum inhibitory concentration (MIC) of oxacillin for MRSA was performed with agar dilution method and eventually polymerase chain reaction (PCR) for mecA gene. Findings: Out of 114 samples, 35 isolates had mecA gene that were assessed with agar dilution method. According to the Clinical and Laboratory Standards Institute (CLSI), MIC of oxacillin in agar dilution method was 8 µg/ml and results was recorded. MecA gene PCR was conducted for all strains and the results were compared with agar dilution method. From resistant isolates, 4% of the strains had mecA gene but were susceptible to methicillin in phenotypic method. Conclusion: Our study showed agar dilution method to be more sensitive and specific than disk diffusion method. PCR is the best method to indentify susceptible and resistant strains to methicillin. Some strains were susceptible to oxacillin in phenotypic method but their mecA gene was identified with PCR.
