Clinical evaluation in detecting methicillin-resistant Staphylococci with cefoxitin disk diffusion method

Objective To evaluate the clinical practicability of cefoxitin disk diffusion method in detecting methicillin-resistant Staphylococci.Methods 163 strains of clinically isolated Staphylococci were tested.The cefoxitin,oxacillin disk diffusion test and PCR amplification of mecA gene were performed simultaneously.The method of PCR was used as the golden standard.Results 163 strains of clinically isolated Staphylococci were tested by PCR.The positive ratio of mecA gene was 81.0%,The ocurrence rate of methicillin-resistant S.aureus(MRSA) and (methicillin-resistant coagulase-negative Staphylococci(MRCNS) was 74.1% and 83.8%,respectively.The cefoxitin,oxacillin disk diffusion and PCR were high consistency in detecting mecA gene.Both sensitivity and specificity were 100%,But cefoxitin disk diffusion was better for methicillin-resistant coagulase-negative Staphylococci.The sensitivity was 100% and 96.0%,the specificity was 94.3% and 88.0%,respectively.Conclusion Cefoxitin disk diffusion has high sensitivity in detecting methicillin-resistant Staphylococci,but for methicillin-resistant coagulase-negative Staphylococci which mecA gene is negative,5% strain may be reported as MRCNS by mistake.Since cefoxitin disk diffusion method is simple,and has higer sensitivity and specificity than oxacillin disk diffusion method in detecting MRS,the result has good correlation with PCR in detecting mecA gene.It may be applied in clinical microbiology laboratory.