Comparison of three phenotypic techniques for detection of methicillin resistance in Staphylococcus spp. reveals a species-dependent performance.
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.
John
Michael A
MA
London Health Sciences Centre, London, Ontario, Canada.
Burden
Julia
J
Stuart
J Ian
JI
Reyes
Romina C
RC
Lannigan
Robert
R
Milburn
Sue
S
Diagre
Deb
D
Wilson
Bev
B
Hussain
Zafar
Z
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
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