Differentiationo Methicillin-Resistant and Methicillin-Susceptible Staphylococcus Aureus and Coagulase-Negative Staphylococci using Cefoxitin

Detection of the mecA gene or PBP2a is considered the gold standard for detecting mecA-mediated methicillin resistance in staphylococci. Among available phenotypic methods, the Clinical and Laboratory Standards Institute (CLSI) has introduced the cefoxitin disk diffusion (DD) test for predicting the presence of mecA in S. aureus and CoNS, which is preferred over the oxacillin DD test. Automated systems are widely used for species identification and susceptibility testing. The BD Phoenix system was compared to the cefoxitin disk diffusion test and oxacillin disk diffusion test for detection of methicillin resistance in 486 clinical specimens. Phoenix sensitivity and Specificity were 100%. The cefoxitin DD test also was much easier to read and did not require the use of transmitted light for detection of resistance.