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 mu g/ml for mecA-negative and >= 6 or 8 mu g/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 mu g/ml for mecA-negative and >= 4 mu g/ml for mecA-positive isolates gave sensitivity and specificity of 94 to 99% and 69 to 80%, respectively.