Comparison of Disk Diffusionand "PCR" methods for determination of Methicillin- resistant Staphylococcus Aureus (MRSA) strains

Increasing prevalence of Methicillin-resistant Staphylococcus aureus (MRSA) in different communities is clearly visible. Because of this, treatment of patients with infections caused by those bacteria has fallen into critical troubles. Current study, therefore, is aimed to compare phenotypic (disk diffusion) and genotypic (PCR) methods for fast diagnosis of methicillin-resistant strains, isolated from patients of Arak Central Hospital. In a cross sectional study whithin one year of period, a total of 100 samples were taken and tested from the patients of Arak hospital (located in the central part of Iran). Isolate's sensitivity to Cefoxitin Disk and Oxacillin was confirmed through disk diffusion. Using PCR, the isolates were tested for the presence of mecA gene. Results were compared from the points of sensitivity and specificity by application of chi square test in SPSS software. Seventy five) 75%) out of the total 100 samples (through oxacillin disk diffusion method, already isolated from patients were resistant to oxacillin. Meanwhile, 83(83%) of cefoxitin disk diffusion method samples’ were resistant to cefoxitin. Three resistant samples to cefoxitin were negative for mecA gene and 80 (80%) samples were positive for mecA gene using PCR. Sensitivity were respectively 93.75%, 100%, and specificity were 100% and 100%, 85%, 100 Findings indicate that oxacillin disk diffusion method is a simple phenotypic method, however, it has lower sensitivity compared to cefoxitin disk diffusion and polymerase chain reaction (PCR) methods. Therfore, it is not recommended for detection of Methicillin-resistant Staphylococcus aureus (MRSA). Existence of strains resistant to cefoxitin without mecA gene, shows the outset of another type of resistance or mutation in Methicillin-resistant Staphylococcus aureus (MRSA).