Correlation of Cefoxitin MICs with the Presence of mecA in Staphylococcus spp

This report describes the results of an 11-laboratory study to determine if a cefoxitin broth microdilution MIC test could predict the presence of mecA in staphylococci. Using breakpoints of ≤4 μg/ml for mecA -negative and ≥6 or 8 μg/ml for mecA -positive isolates, sensitivity and specificity based on mecA or presumed mecA for Staphylococcus aureus at 18 h of incubation were 99.7 to 100% in three cation-adjusted Mueller-Hinton broths tested. For coagulase-negative strains at 24 h of incubation, breakpoints of ≤2 μg/ml for mecA -negative and ≥4 μg/ml for mecA -positive isolates gave sensitivity and specificity of 94 to 99% and 69 to 80%, respectively.