Journal Article

Evaluation of different methods for detecting methicillin (oxacillin) resistance in <i>Staphylococcus aureus</i>

David Velasco, Maria del Mar Tomas, Monica Cartelle, Alejandro Beceiro, Astrid Perez, Francisca Molina, Rita Moure, Rosa Villanueva and German Bou

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 55, issue 3, pages 379-382
Published in print March 2005 | ISSN: 0305-7453
Published online March 2005 | e-ISSN: 1460-2091 | DOI: http://dx.doi.org/10.1093/jac/dki017
Evaluation of different methods for detecting methicillin (oxacillin) resistance in Staphylococcus aureus

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  • Medical Oncology
  • Critical Care

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Objectives: To evaluate the performance of oxacillin, cefazolin, cefoxitin, cefotaxime and imipenem discs; Etest for oxacillin; microdilution; agar screening plates with 2 and 6 mg/L of oxacillin; and PBP2′ agglutination for detection of methicillin-resistant Staphylococcus aureus (MRSA).

Methods: A total of 102 clinical S. aureus isolates, including 51 MRSA isolates, tested by PCR for the presence or absence of the mecA gene (gold standard method), isolated from different patients and at different times, were tested with: oxacillin (1 μg), cefazolin, cefoxitin, cefotaxime and imipenem (all 30 μg) discs; Etest for oxacillin; microdilution with oxacillin; agar screening tests (ORSAB medium) with 2 mg/L or 6 mg/L of oxacillin; and PBP2′ agglutination with two different kits for detection of MRSA strains.

Results: The cefoxitin disc, ORSAB medium and PBP2′ detection all showed 100% sensitivity. The cefoxitin, cefazolin and imipenem discs, Etest for oxacillin, microdilution and agar screening method with 6 mg/L at 24 h showed the highest specificity (100%), although variable degrees of sensitivity. The cefoxitin disc, which showed negative and positive predictive values of 100% and 98%, respectively was the best method for detecting MRSA isolates.

Conclusions: In the absence of availability of molecular biology techniques, the cefoxitin disc was the best predictor of methicillin resistance in S. aureus from among the techniques tested.

Keywords: MRSA; S. aureus; detection

Journal Article.  2548 words. 

Subjects: Medical Oncology ; Critical Care

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