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Journal of Clinical Microbiology, September 2002, p. 3291-3295, Vol. 40, No. 9
0095-1137/02/$04.00+0     DOI: 10.1128/JCM.40.9.3291-3295.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Rapid Detection of Methicillin Resistance in Coagulase-Negative Staphylococci with the VITEK 2 System

Matthias A. Horstkotte,* Johannes K.-M. Knobloch, Holger Rohde, Sabine Dobinsky, and Dietrich Mack

Institut für Medizinische Mikrobiologie und Immunologie, Universitätsklinikum Hamburg-Eppendorf, D-20246 Hamburg, Germany

Received 4 April 2002/ Returned for modification 16 May 2002/ Accepted 23 June 2002

The aim of the present study was to evaluate the accuracy of the new VITEK 2 system (bioMérieux, Marcy l' Etoile, France) for the detection of methicillin resistance in coagulase-negative staphylococci (CoNS) by using AST-P515 and AST-P523 test cards. Analyses of the VITEK 2 oxacillin MIC determination evaluated according to the actual breakpoint (>=0.5 µg/ml) of the National Committee for Clinical Laboratory Standards resulted in a high sensitivity of 99.2% but a moderate specificity of 80%. The newly included oxacillin resistance (OR) test of the VITEK 2 system displayed a high sensitivity and a high specificity of 97.5 and 98.7%, respectively. Concordance between the results of the mecA PCR and the VITEK 2 oxacillin MIC was observed for almost all Staphylococcus epidermidis strains, but the reduced specificity was attributable to higher oxacillin MICs for mecA-negative non-S. epidermidis strains, especially S. saprophyticus, S. lugdunensis, and S. cohnii. Evaluation of alternative oxacillin MIC breakpoints of 1, 2, or 4 µg/ml resulted in improved degrees of specificity of 84, 90.7, and 97.3%, respectively. Only minor changes occurred in the corresponding sensitivity values, which were 98.4, 97.5, and 97.5%, respectively. Methicillin resistance in CoNS was detected after 7 and 8 h in 91.1 and 93.5% of the mecA-positive strains, respectively, by the VITEK 2 OR test and in 86.3 and 89.5% of the mecA-positive strains, respectively, by VITEK 2 oxacillin MIC determination. After 7 and 8 h the VITEK 2 OR test classified 59.2 and 78.9% of the mecA-negative strains, respectively, as susceptible to oxacillin, whereas comparable values were obtained 2 h later by VITEK 2 oxacillin MIC determination. The results of our study encourage the use of the VITEK 2 system, which proved to be a highly reliable and rapid phenotypic method for the detection of methicillin resistance in CoNS.

* Corresponding author. Mailing address: Institut für Medizinische Mikrobiologie und Immunologie, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52 D-20246, Hamburg, Germany. Phone: 49 40/42803-3147. Fax: 49 40/42803-4881. E-mail: horstko{at}uke.uni-hamburg.de.

Journal of Clinical Microbiology, September 2002, p. 3291-3295, Vol. 40, No. 9
0095-1137/02/$04.00+0     DOI: 10.1128/JCM.40.9.3291-3295.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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