Validation of VITEK 2 Version 4.01 Software for Detection, Identification, and Classification of Glycopeptide-Resistant Enterococci

Abstract

We evaluated the ability of the new VITEK 2 version 4.01 software to identify and detect glycopeptideresistant enterococci compared to that of the reference broth microdilution method and to classify them into the vanA, vanB, vanC1, and vanC2 genotypes. Moreover, the accuracy of antimicrobial susceptibility testing with agents with improved potencies against glycopeptide-resistant enterococci was determined. A total of 121 enterococci were investigated. The new VITEK 2 software was able to identify 114 (94.2%) enterococcal strains correctly to the species level and to classify 119 (98.3%) enterococci correctly to the glycopeptide resistance genotype level. One Enterococcus casseliflavus strain and six Enterococcus faecium vanA strains with low-level resistance to vancomycin were identified with low discrimination, requiring additional tests. One of the vanA strains was misclassified as the vanB type, and one glycopeptide-susceptible E. facium wild type was misclassified as the vanA type. The overall essential agreements for antimicrobial susceptibility testing results were 94.2% for vancomycin, 95.9% for teicoplanin, 100% for quinupristin-dalfopristin and moxifloxacin, and 97.5% for linezolid. The rates of minor errors were 9% for teicoplanin and 5% for the other antibiotic agents. The identification and susceptibility data were produced within 4 h to 6 h 30 min and 8 h 15 min to 12 h 15 min. In conclusion, use of VITEK 2 version 4.01 software appears to be a reliable method for the identification and detection of glycopeptide-resistant enterococci as well as an improvement over the use of the former VITEK 2 database. However, a significant reduction in the detection time would be desirable.The first glycopeptide-resistant enterococci (GRE) that harbored the vanA transposon were identified in 1987 in Europe (10). Within 10 years GRE represented Ͼ25% of the enterococci that cause bloodstream infections in hospitalized patients in the United States (2). The vanA and vanB genotypes (two genetically distinct forms of resistance) are recognized to be clinically important, whereas GRE strains harboring the intrinsic resistance genes vanC1 and vanC2 seem to play a less important clinical role. Contrary to the rates in other countries, the rates of GRE in German hospitals are low and GRE account for only about 1% of enterococcal isolates (8), but increasing rates in stool and clinical samples were reported recently (1, 17). Moreover, the numbers of nosocomial infections and the rates of transmission of GRE have increased (17). As GRE infections appear to be more deadly and more costly than infections caused by vancomycin-susceptible strains (15), rapid and reliable results of identification and antimicrobial susceptibility testing (AST) are necessary for the adequate treatment of infections caused by GRE and the prevention of transmission of GRE strains.Many laboratories worldwide have adopted the VITEK automated system (bioMérieux, Nürtingen, Germany) for the detection of GRE strains in routine clinical microbiology. E...

Use of the Phoenix Automated System for Identification of Streptococcus and Enterococcus spp

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