Evaluation of accuracy and cost of four different methods for detection of methicillin resistance in Staphylococcus aureus isolates from pediatric patients hospitalized in Brazil

Abstract

We studied 70 pediatric clinical isolates of Staphylococcus aureus to perform a comparison of different methods for detection of methicillin-resistant S. aureus (MRSA) using polymerase chain reaction for mecA as the “gold standard” assay. The isolates were tested with oxacillin and cefoxitin discs, oxacillin agar screening plate and E-test. Of the 70 strains, 43 were mecA-positive and 27 mecA-negative. Oxacillin agar screening plate and E-test had 100% sensitivity and specificity for the presence of mecA gene. We found a specificity of 96% for both disc-diffusion methods, and sensitivities of 95% (oxacillin disc) and 93% (cefoxitin disc). However, with the new Clinical and Laboratory Standards Institute 2007 cefoxitin breakpoints the sensitivity of this method would be increased to 100%, without any decrease in specificity. These results show how important is the evaluation of the available microbiological methods by different laboratories in different settings.

Keywords

MRSA - disc diffusion - mecA