title: Phenotypic detection of mecC-MRSA: cefoxitin is more reliable than oxacillin.
abstract: OBJECTIVE
  To investigate the reliability of cefoxitin and oxacillin for the detection of mecC-positive Staphylococcus aureus.
  
  
  METHODS
  The susceptibility to cefoxitin and oxacillin of 62 mecC-positive S. aureus isolates was investigated using broth microdilution, agar dilution, Etest and disc diffusion on different types of media. The data were interpreted for the utility of cefoxitin and oxacillin in conjunction with the stated methodologies for the detection of mecC-positive isolates.
  
  
  RESULTS
  Cefoxitin with Mueller-Hinton media from Becton Dickinson and Oxoid detected all mecC-positive isolates when tested by broth microdilution, agar dilution and disc diffusion. By Etest, one isolate was falsely susceptible. Mueller-Hinton agar from bioMérieux was substantially less able to detect these isolates. One isolate was falsely susceptible by agar dilution when using Iso-Sensitest and Columbia agar. Disc diffusion using cefoxitin on Iso-Sensitest agar missed 29% of the isolates. For oxacillin, only agar dilution on Columbia agar + 2% NaCl was able to detect all mecC-positive isolates successfully.
  
  
  CONCLUSIONS
  Cefoxitin used with EUCAST methodology and oxacillin used with agar dilution on Columbia agar + 2% NaCl detected all mecC-positive isolates. These methods with their concomitant agars should be preferred over Iso-Sensitest, which is recommended by the BSAC. It should be noted that for disc diffusion Mueller-Hinton media from bioMérieux performed poorly, with 26%-47% of mecC isolates being falsely susceptible.
authors.affiliation: Department of Microbiology and Infection Control, Statens Serum Institut, Artillerivej 5, Copenhagen 2300, Denmark.
authors.forename: Robert
authors.initials: R
authors.lastname: Skov
authors.forename: Anders Rhod
authors.initials: AR
authors.lastname: Larsen
authors.forename: Angela
authors.initials: A
authors.lastname: Kearns
authors.forename: Mark
authors.initials: M
authors.lastname: Holmes
authors.forename: Christopher
authors.initials: C
authors.lastname: Teale
authors.forename: Giles
authors.initials: G
authors.lastname: Edwards
authors.forename: Robert
authors.initials: R
authors.lastname: Hill
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002440:Cefoxitin / Q000494:pharmacology*; D003470:Culture Media / Q000737:chemistry; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests / Q000379:methods; D010068:Oxacillin / Q000494:pharmacology*; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D002440:Cefoxitin; D010068:Oxacillin
keywords: Staphylococcus aureus; methicillin resistance; susceptibility testing