Comparison of Methods for Detecting Methicillin-Resistant Coagulase-Negative Staphylococci in Device-Associated Infections

Abstract

Background: Coagulase-negative Staphylococci (CoNS) is one of the major causes of infections in hospitals. Methicillin resistance has greatly increased in different CoNS species in previous years. Here, we evaluated the performance of four phenotypic tests for detecting mecA-mediated methicillin resistance rate in CoNS isolated from different device-associated infections in Tanta University Hospitals, Egypt. Methodology: One hundred and fifteen CoNS isolates were examined for mecA-mediated methicillin resistance using polymerase chain reaction (PCR) as the standard gold test. Susceptibility to methicillin was investigated using VITEK 2 assay, oxacillin broth microdilution, and cefoxitin disc diffusion tests. Results: Of all isolates, 98.3% were mecA-positive. The sensitivities of the different methods examined were as follows: 100% for the VITEK cefoxitin test, 97.4% for the VITEK oxacillin test, 93.8% for the oxacillin broth microdilution, and 82.3% for the cefoxitin disc diffusion test. The test specificity could not be accurately determined because of the small number of mecA-negative isolates (n = 2). Conclusion: The rate of methicillin resistance reached 98.3% among CoNS isolates. Our results demonstrate that the VITEK 2 assay is rapid and has high sensitivity compared to other phenotypic methods for detecting methicillin resistance among different species of CoNS. Therefore, we recommend the dual measurement of both cefoxitin and oxacillin susceptibilities using the VITEK 2 assay for best results.