title: Comparison of three phenotypic techniques for detection of methicillin resistance in Staphylococcus spp. reveals a species-dependent performance.
abstract: OBJECTIVE
  To evaluate the usefulness of the cefoxitin screen in Vitek 2 Gram-positive panels for recognizing methicillin-resistant strains of staphylococci.
  
  
  METHODS
  Seven hundred and ninety-nine non-duplicate isolates of Staphylococcus aureus and coagulase-negative strains were included in the study. Methicillin resistance was measured using PCR for the mecA gene, the CLSI cefoxitin disc diffusion method, the Vitek 2 cefoxitin screen and the Vitek 2 oxacillin susceptibility test.
  
  
  RESULTS
  Compared with the molecular detection of methicillin resistance the overall sensitivities and specificities of the phenotypic tests for cefoxitin disc diffusion were 94.9% and 97.0%, for Vitek 2 cefoxitin screen were 94.6% and 93.5% and for Vitek 2 oxacillin susceptibility test were 93.8% and 77.9%. The cephamycin tests (cefoxitin disc diffusion and Vitek 2 screen) were not able to identify mecA-positive strains of Staphylococcus simulans. In addition, the performance of the Vitek 2 system was poor against Staphylococcus cohnii subspecies, Staphylococcus hominis hominis and Staphylococcus saprophyticus.
  
  
  CONCLUSIONS
  Overall, the performance of the Vitek 2 system for differentiating mecA-positive staphylococci was comparable to PCR and the CLSI disc diffusion method; however, performance was species-dependent. Thus, before accepting the results produced by Vitek 2, species identification may be required.
authors.affiliation: London Health Sciences Centre, London, Ontario, Canada.
authors.forename: Michael A
authors.initials: MA
authors.lastname: John
authors.forename: Julia
authors.initials: J
authors.lastname: Burden
authors.forename: J Ian
authors.initials: JI
authors.lastname: Stuart
authors.forename: Romina C
authors.initials: RC
authors.lastname: Reyes
authors.forename: Robert
authors.initials: R
authors.lastname: Lannigan
authors.forename: Sue
authors.initials: S
authors.lastname: Milburn
authors.forename: Deb
authors.initials: D
authors.lastname: Diagre
authors.forename: Bev
authors.initials: B
authors.lastname: Wilson
authors.forename: Zafar
authors.initials: Z
authors.lastname: Hussain
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D002440:Cefoxitin / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000235:genetics; D006801:Humans; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests / Q000379:methods; D010068:Oxacillin / Q000494:pharmacology; D046915:Penicillin-Binding Proteins; D016133:Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D013210:Staphylococcus / Q000187:drug effects* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C487495:MecA protein, Staphylococcus epidermidis; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus; D002440:Cefoxitin; D010068:Oxacillin