Comparison of Different Phenotypic Approaches to Screen and Detect mecC-Harboring Methicillin-Resistant Staphylococcus aureus

André Kriegeskorte, Evgeny A Idelevich, Andreas Schlattmann, Franziska Layer, Birgit Strommenger, Olivier Denis, Gavin K Paterson, Mark A Holmes, Guido Werner, Karsten Becker

Research output: Contribution to journalArticlepeer-review

Abstract

Similar to mecA, mecC confers resistance against beta-lactams, leading to the phenotype of a methicillin-resistant Staphylococcus aureus (MRSA). However, mecC-harboring MRSA pose special difficulties in their detection. The aim of this study was to assess and compare different phenotypic systems for screening, identification, and susceptibility testing of mecC-positive MRSA isolates. A well-characterized collection of mecC-positive S. aureus isolates (n = 111) was used for evaluation. Routinely used approaches were studied to determine their suitability to correctly identify mecC-harboring MRSA including three (semi-)automated antimicrobial susceptibility testing (AST) systems and five selective chromogenic agar plates. Additionally, a cefoxitin disk diffusion test and an oxacillin broth microdilution assay were examined. All mecC-harboring MRSA isolates were able to grow on all chromogenic MRSA screening plates tested. Detection of these isolates in AST systems based on cefoxitin and/or oxacillin testing yielded overall positive agreement with the mecC genotype of 97.3 % (MicroScan WalkAway™, Siemens), 91.9 % (Vitek 2®, bioMérieux), and 64.9 % (Phoenix™, BD). The phenotypic resistance pattern most frequently observed by AST devices was "cefoxitin resistance/oxacillin susceptibility", ranging from 54.1 % (Phoenix) over 83.8 % (Vitek 2) to 92.8 % (WalkAway). The cefoxitin disk diffusion and oxacillin broth microdilution assays categorized 100 % and 61.3 % of isolates to be MRSA, respectively. The chromogenic media tested confirmed their suitability to reliably screen for mecC-harboring MRSA. The AST systems showed false-negative results with varying numbers, misidentifying mecC MRSA as methicillin susceptible S. aureus This study underlines cefoxitin's status as the superior surrogate mecC MRSA marker.

Original languageEnglish
JournalJournal of Clinical Microbiology
Early online date4 Oct 2017
DOIs
Publication statusE-pub ahead of print - 4 Oct 2017

Keywords

  • MRSA
  • Staphylococcus aureu
  • broth microdilution
  • cefoxitin
  • chromogenic media,
  • disk diffusion

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