Objective: Methicillin- resistant Staphylococcus aureus (MRSA) is a major health concern worldwide as one of the predominant pathogens in nosocomial infections. Although Polymerase Chain Reaction (PCR) is the gold standard method for the detection of mecA gene which codes methicillin resistance, limited opportunities in routine microbiology laboratories restrict the use of PCR. Therefore, phenotypic methods for the detection of MRSA still have an important role in diagnosis. The aim of this study is to compare the phenotypic methods used to determine methicillin resistance of S. aureus strains isolated from various clinical samples at Başkent University Medical Microbiology Laboratory.

Material and Methods: A total of 118 S. aureus isolates were analyzed in the study. By using cefoxitin disc diffusion (CDD) method 50 of these isolates were found to be methicillin- resistant and 68 were methicillin- susceptible. Chromogenic medium, gradient diffusion test and oxacillin screening agar were used for the detection of methicillin resistance, and CDD was accepted as the reference method.

Results: The sensitivities, and specificities of oxacillin screening agar, chromogenic medium and gradient diffusion test were 100%, 96% and 92% vs 91%, 7% and 100%, respectively. According to these results the detection of methicillin resistance by chromogenic media was not found to be statistically significant (p=0.697). Detection of methicillin resistance by the other phenotypic methods was detected to be statistically significant (p<0.001). The costs of the methods used based on decreasing amounts of expenses are gradient diffusion test, chromogenic media, oxacillin screening agar and cefoxitin disc diffusion test.

Conclusion: All of the phenotypic methods employed in this study can be used for the detection of methicillin resistance in routine microbiology laboratories, however since false- positive results can be obtained with chromogenic media, it has been concluded that especially positive isolates detected in CDD method should be reevaluated, and confirmed by using other phenotypic methods.