Evaluation of the CLSI cefoxitin 30-microg disk-diffusion method for detecting methicillin resistance in...

Methicillin susceptibility of 415 staphylococcal isolates from Chinese hospitals was assessed using the CLSI disk-diffusion method with a cefoxitin 30-microg disk in comparison with an oxacillin 1-microg disk. PCR-based detection of mecA was the reference standard. The cefoxitin 30-microg disk performed with almost the same high level of accuracy as the oxacillin 1-microg disk in detecting methicillin resistance in Staphylococcus aureus. For coagulase-negative staphylococci (CoNS), the sensitivity of the cefoxitin 30-microg disk was 90.5%, compared with 83.4% for the oxacillin 1-microg disk. Confirmatory testing of isolates with borderline susceptibility and revision of the cefoxitin breakpoint are proposed in order to categorise CoNS more accurately.