Evaluation of a new system, VITEK 2, for identification and antimicrobial susceptibility testing of enterococci

We evaluated the new automated VITEK 2 system (bioMerieux) for the identifi cation and antimicrobial susceptibility testing of enterococci, The results obtained with the VITEK 2 system were compared to those obtained by refere nce methods: standard identification by the scheme of Facklam and Sahm (R. R. Facklam and D. F. Sahm, p. 308-314, in P. R. Murray et al,, ed., Manual of Clinical Microbiology, 6th ed., 1995] and with the API 20 STREP system a nd, for antimicrobial susceptibility testing, broth microdilution and agar dilution methods by the procedures of the National Committee for Clinical L aboratory Standards. The presence of vanA and vanB genes was determined by PCR, A total of 150 clinical isolates were studied, corresponding to 60 Ent erococcus faecalis, 55 Enterococcus faecium, 26 Enterococcus gallinarum, 5 Enterococcus avium, 2 Enterococcus durans, and 2 Enterococcus raffinosus is olates. Among those isolates, 131 (87%) were correctly identified to the sp ecies level with the VITEK 2 system. Approximately half of the misidentific ations were for E. faecium with low-level resistance to vancomycin, identif ied as E. gallinarum or E. casselifiavus; however, a motility test solved t he discrepancies and increased the agreement to 94%, Among the strains stud ied, 66% were vancomycin resistant (57 VanA, 16 VanB, and 26 VanC strains), 23% were ampicillin resistant (MICs, greater than or equal to 16 mu g/ml), 31% were high-level gentamicin resistant, and 45% were high-level streptom ycin resistant. Percentages of agreement for susceptibility and resistance to ampicillin, vancomycin, and teicoplanin and for high-level gentamicin re sistance and high-level streptomycin resistance were 93, 95, 97, 97, and 96 %, respectively. The accuracy of identification and antimicrobial susceptib ility testing of enterococci with the VITEK 2 system, together with the sig nificant reduction in handling time, will have a positive impact on the wor k flow of the clinical microbiology laboratory.