Phenotypic and Molecular Detection of Methicillin Resistance in S. aureus

Abstract

Detecting methicillin resistance is complicated due to the heterogeneity of its phenotypic expression, making its detection difficult in the laboratory; this has led to the development of several techniques to increase its expression in vitro. Four techniques for detecting methicillin resistance were evaluated: the disk diffusion method with oxacillin (OX, 1 μg) and cephoxitin (FOX, 30 μg); the screening test, minimum inhibitory concentration (MIC) and detection of PBP2a, using the presence of mecA gen as a reference method; 286 strains of S. aureus, were processed. The sensibility (SEN), specificity (SPE), positive predictive value (PPV), negative predictive value (NPV) and efficiency (EFC) of each method were determined. A total of 50 oxacillin resistant, PBP2a positive (mecA positive) strains were obtained. Sensibility of the OX disk was 99.14%; and of the FOX disk was 100%. The SEN, PPV, NVP and EFC of the other methods were 100%. All the tests, except the OX disk diffusion method (99.14% of ESP), were 100% specific.

Keywords

• S. aureus, resistencia ameticilina, métodos fenotípicos,métodos moleculares