Detection of MecA Mediated Methicillin Resistance in Staphylococcus aureus by Cefoxitin Disc Diffusion Method and Latex Agglutination Test

Aim: To assess the accuracy of cefoxitin disk diffusion method and PBP2a latex agglutination test for detection of methicillin resistance in Staphylococcus aureus. Study Design: Descriptive Study Place and duration of study: Pathology Department, Post Graduate Medical Institute, Lahore from February 2013 to October 2013 Methods: A total of 130 Staphylococcus aureus isolates from different clinical specimens were tested for methicillin resistance by disk diffusion method. Disk diffusion method was performed using cefoxitin (FOX) 30 mu g disc on Mueller Hinton agar (MHA) and incubation was done at 35 degrees C for 24 hours. Results were interpreted according to CLSI recommendations. Confirmation of MRSA strains was done by PBP2a latex agglutination test. Results: The results of the study showed that out of 130 Staphylococcus aureus isolates, 54 were cefoxitin resistant, but 4 isolates were mecA gene product (PBP2a) negative when they were confirmed with PBP2a latex agglutination kit. So, 4(7.41%) mecA -ve isolates were falsely identified as MRSA by cefoxitin disc Diffusion method. Conclusion: Latex agglutination test was a rapid and accurate method and could be the best predictor to detect MRSA when the molecular methods are not available.