Evaluation of Cefoxitin Disc Diffusion and Chromogenic Agar in the Detection of Methicillin Resistant Staphylococcus aureus

Methicillin resistant Staphylococcus aureus (MRSA) has a worldwide distribution and is an important cause of clinical and epidemiological problems. The aim of this study was to evaluate the usefulness of some phenotypic methods for the detection of methicillin resistant S. aureus in clinical laboratories. The study is cross sectional. A total of 93 S. aureus isolates were tested using cefoxitin disk diffusion (CDD) and oxacillin resistance screening agar base (ORSAB) with reference to mecA gene PCR. Of the 93 isolates, CDD test showed 34 were MRSA, while ORSAB recorded 42. MecA gene was detected by PCR in 34 of the isolates. The CDD showed 97.1% sensitivity and 98.3% specificity and therefore superior to ORSAB with sensitivity 97.1% and specificity 84.7%. The cefoxitin disk test required no special test conditions and can improve the reliability of routine tests for the detection of MRSA. CDD test can thus be used as a cheap and reliable alternative to PCR for the detection of MRSA in resources limited settings.