Comparison of mecA gene-based PCR with CLSI cefoxitin and oxacillin disc diffusion methods for detecting methicillin resistance in Staphylococcus aureus clinical isolates

Abstract

The emergence of heterogeneous populations of methicillin-resistant Staphylococcus aureus (MRSA) causes major problems in routine screening for MRSA. Cefoxitin is a potent inducer of the mecA regulatory system and can be use for detection of heterogeneous populations of MRSA. Detection of the mecA gene by PCR was considered to be the "gold standard". In this study we determined the sensitivity and specificity of the oxacillin disk diffusion test, cefoxitin disk diffusion test and oxacillin agar screening for detection of MRSA. A total of 124 non-duplicate isolates of S. aureus were included in the study. Methicillin resistance was measured using oxacillin (1μg) and cefoxitin(30μg) disc diffusion method and oxacillin agar screening test (6 mg/ml oxacillin) according to CLSI guideline and PCR for the mecA gene. Compared with the molecular detection of methicillin resistance the overall sensitivities and specificities of the phenotypic tests for cefoxitin disc diffusion were 100%, for oxacillin disc diffusion were 91.7 and 92.8% and for oxacillin agar screening were 95 and 95.5%, respectively. We concluded that in the absence of availability of molecular biology techniques, the cefoxitin disc was the best detector of methicillin resistance in S. aureus related to the other phenotypic tests.

Epidemiology of clinically isolated methicillin-resistant Staphylococcus aureus (MRSA) and its susceptibility to linezolid and vancomycin in Egypt: a systematic review with meta-analysis

“…The cefoxitin disc diffusion test results were found to be consistent with PCR identification of the mecA gene, similar to previous studies [ 12 , 86 – 89 ]. Both CDD and PCR were at the same point of estimate (66%) of MRSA prevalence in the studies that used CDD and/or PCR for MRSA identification, 34 and 31 studies, respectively.…”

Phenotypic and Genotypic Characterization of Methicillin Resistance in Staphylococci Isolated from an Egyptian University Hospital

“…Among the phenotypic techniques used in this study to identify methicillin resistance in S. aureus isolates the cefoxitin disc diffusion test exhibited the best diagnostic performance, with 100% sensitivity compared to mecA PCR. Similar results were reported by many researchers who used PCR as a reference method [77][78][79], while Perazzi et al and Martins et al [80,81] reported lower sensitivities of 80% and 91.3%, respectively. We detected that cefoxitin disc was superior to oxacillin, consistent with previous reports [82,83].…”