Comparison Of Disk Diffusion Method With Polymerase Chain Reaction For Detecting Methicillin Resistance In Clinical Isolates Of Staphylococci

Staphylococci as a micro-organism, has the most importance to cause nosocomial infections, particularly in patients with indwelling catheters or other medical devices. Unfortunately 90% of Staphylococci isolated from the nosocomial infections are resistant to methicillin, and methicillin resistance strains are also resistant to a wide range of antimicrobial drugs, therefore detecting of these strains are valuable to eradicate the infection elements. Despite guidelines published by the national committee for clinical laboratory standards (NCCLS) for testing of susceptibility to methicillin for Staphylococci, the phenotypic method for detecting methicillin resistance remains controversial. Therefore, the genetic assays have been used to detect antimicrobial susceptibility of Staphylococci to methicillin. Resistance to methicillin is coded by mec A gene in staphylococcus, and this gen must be detected in genetic assays. In this study 155 clinical staphylococcal isolates (70 coagulase- negative staphylococcus and 85 coagulase- Positive staphylococci) were evaluated for susceptibility to methicillin by using disk diffusion method.ResuIts& Methicillin resistance was shown in 62 coagulase- negative staphylococcus (72.9%) and 27 coagulas positive staphylococcus (38.6%) but 63 coagulase negative Staphylococci (74%) and 28 coagulase positive isolates with mec a gene associated resistance were detected by PCR method. The results of this test were compared to the results for mec A gene detection by PCR test as a gold standard. The sensitivity, specifity and accuracy of the disk diffusion test for coagulase-negative staphylococcus were 96.8%, 95.45% and 96.47% and for coagulase positive staphylococci were 98.43%, 95.45% and 98.32% respectively.