Evaluation of different methods for the rapid diagnosis of methicillin-resistance in Staphylococcus aureus


Sadaka S. M., El-Ghazzawy E. F., Harfoush R. A.* and Meheissen M. A.

Since its first identification in the early 1960s, Methicillin-Resistant Staphylococcus aureus (MRSA) has been recognized as a major human pathogen. The aim of this study was to identify the prevalence of MRSA in Alexandria Main University Hospital and to settle on a simple, rapid, accurate and costeffective phenotypic test for the detection of MRSA from clinical specimens. One hundred S. aureus isolates, including 71 MRSA isolates, as confirmed by PCR for the presence or absence of the mecA gene as the gold standard, were isolated from patients from different departments at Alexandria Main University Hospital over a six month-period. They were tested for methicillin resistance by comparing five phenotypic tests (Mannitol salt agar-cefoxitin [MSA-FOX] , oxacillin disc diffusion, cefoxitin disc diffusion, oxacillin MIC by broth microdilution and latex agglutination for PBP2a) to the gold standard genotypic test (detection of mecA gene by PCR). It was found that both oxacillin disc diffusion and latex agglutination showed 100% sensitivity, negative and positive predictive values of 100 and 97.3%, respectively. Both were found to be highly sensitive phenotypic tests for the detection of MRSA. However, the oxacillin disc diffusion test is much more cost-effective. The MSA-FOX, whose sensitivity was 95.8%, was found to be a highly sensitive, cost-effective screening medium for the detection of MRSA.

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