Identification and detection of methicillin resistance in Non-Epidermidis coagulase-negative staphylococci

ABSTRACT

The NCCLS (2004) presented a new methodology to detect, by disk-diffusion agar, oxacillin-resistance using a cefoxitin disk. We identified coagulase-negative staphylococci (SCoN) to the species level and compared the use of cefoxitin disks (30 µg) with oxacillin disks (1 µg), agar dilution (minimum inhibitory concentration of oxacillin) and mecA gene detection in isolates of coagulase-negative bacteria other than Staphylococcus epidermidis (SCoNne). A total of 238 SCoNne was evaluated; oxacillin-resistance (the mecA gene) was detected in 71 percent of the isolates. All methods gave 100 percent sensitivity, based on presence of the mecA gene. The specificity of the cefoxitin disk was 100 percent, while the oxacillin disk gave a specificity of 91 percent and agar dilution oxacillin gave a specificity of 88 percent. We conclude that the cefoxitin disk is an efficient test, and it is an easy method for use in clinical laboratories to detect oxacillin-resistance in staphylococci.