Rapid detection of methicillin resistance in coagulase-negative Staphylococci with the VITEK 2 system.
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 micro g/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 micro g/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.
Horstkotte
Matthias A
MA
Institut für Medizinische Mikrobiologie und Immunologie, Universitätsklinikum Hamburg-Eppendorf, D-20246 Hamburg, Germany. horstko@uke.uni-hamburg.de
Knobloch
Johannes K-M
JK
Rohde
Holger
H
Dobinsky
Sabine
S
Mack
Dietrich
D
D001426:Bacterial Proteins; D002352:Carrier Proteins; D003030:Coagulase / Q000378:metabolism*; D006602:Hexosyltransferases; D006801:Humans; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests / Q000379:methods / Q000592:standards; D002267:Muramoylpentapeptide Carboxypeptidase; D010068:Oxacillin / Q000494:pharmacology; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000494:pharmacology; D010458:Peptidyl Transferases; D011933:Reagent Kits, Diagnostic; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections; D013210:Staphylococcus / Q000187:drug effects*; D013997:Time Factors
D001426:Bacterial Proteins; D002352:Carrier Proteins; D003030:Coagulase; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D011933:Reagent Kits, Diagnostic; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D010068:Oxacillin