Comparison of mecA Polymerase Chain Reaction With Phenotypic Methods for the Detection of Methicillin-Resistant Staphylococcus aureus

In the present study, several conventional methods to detect methicillin-resistant Staphylococcus aureus (MRSA) were compared with polymerase chain reaction (PCR) detection of mecA gene–positive isolates. Cefoxitin E-test was also evaluated as a possible phenotypic method of MRSA detection. Oxacillin agar screen and PBP2′ latex agglutination methods were found to be more sensitive than oxacillin and cefoxitin disk-diffusion methods. Cefoxitin disk diffusion was found to be the most specific. A combination of oxacillin agar screening with cefoxitin disk diffusion, or oxacillin disk diffusion with PBP2′, improved sensitivity and specificity. Cefoxitin E-test with the current break points had low sensitivity and specificity (33.3% and 75%, respectively) for the detection of MRSA. However, changing the break points to ≤ 4 μg/ml and to ≥ 6 μg/ml for sensitive and resistant, respectively, greatly improved both. Changing the 30-μg cefoxitin disk-diffusion break points to ≤ 21 mm for resistant slightly improved sensitivity but had no effect on specificity. It was therefore concluded that the use of more than one screening method is necessary to detect all MRSA isolates in clinical settings.