[Short communication: use of cefoxitin disc diffusion method for the detection of methicillin resistance in Staphylococcus aureus clinical isolates]

Abstract

The aim of this study was to compare the cefoxitin disc diffusion method with oxacillin broth microdilution and agar screening methods for the detection of methicillin-resistant Staphylococcus aureus (MRSA). The presence of PBP2a in 94 S. aureus clinical isolates were screened by latex agglutination MRSA-Screen test (Oxoid Ltd, UK), and 64 (68%) of the strains were found positive. Cefoxitin disc diffusion method and oxacillin broth microdilution and agar screening methods were performed in the guidance of Clinical and Laboratory Standards Institute (CLSI) proposals. All of the 64 PBP2a positive isolates were found resistant, and 30 PBP2a negative isolates were detected as susceptible to oxacillin by both of the broth microdilution and agar screening methods. In cefoxitin disc diffusion method, zone diameters of 62 isolates were measured as 0-14 mm, while two isolates gave 15-17 mm and 30 isolates gave 220 mm zone diameters. According to the CLSI proposals, 64 isolates were accepted as oxacillin-resistant in view of their cefoxitin zone diameters. As a result, the sensitivity and specificity of cefoxitin disc diffusion method was detected as 100%, when comparing with both gold standard (PBP2a presence) method and oxacillin broth microdilution and agar screening methods, indicating that it is a reliable test to investigate oxacillin resistance of clinical S. aureus isolates in routine laboratories where molecular tests could not be performed due to economical reasons.