Comparative evaluation of oxacillin-resistance by four different methods in staphylococci strains isolated from nosocomial infections

Abstract

In this study, 102 staphylococci strains, 39 coagulase positive and 63 coagulase negative, were tested for oxacillin susceptibility by agar screening, microdilution, disk diffusion and automated Sceptor® system according to National Committee for Clinical Laboratory Standarts (NCCLS) recommendations. Tests were compared with each other by using agar screening as a reference method. Oxacillin resistance in staphylococci strains was found to be 60.8%, 57.8%, 58.8%, 54.9% in agar screening, microdilution, disk diffusion and automated Sceptor® system, respectively. The sensitivity, specificity and agreement rates of each test were found as follows when compared with the reference method; for microdilution 95.4%, 93.1%, 94.1%, for disk diffusion 95.3%, 95.2 %, 96.5 %, and for automated Sceptor® system 88.5 %, 88.8% and 87.2% respectively. In conclusion, to detect oxacillin resistance, sensitivity and specificity of automated Sceptor® system was found to be lower when compared to all others. Disk diffusion test can be used instead of agar screening test when it is not available.