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Journal of Clinical Microbiology, Aug 1997, 2115-2119, Vol 35, No. 8
GV Doern, AB Brueggemann, R Perla, J Daly, D Halkias, RN Jones and MA Saubolle
A four-center study in which a total of 1,082 recent clinical isolates of
members of the family Enterobacteriaceae and Pseudomonas aeruginosa were
examined versus 11 antimicrobial agents with the bioMerieux Vitek
susceptibility test system (Hazelwood, Mo.) and the GNS-F6 card was
conducted. In addition, a challenge set consisting of the same 200
organisms was examined in each of the four participating laboratories.
Results obtained with the Vitek system were compared to MICs determined by
a standardized broth microdilution method. For purposes of comparison,
susceptibility categories (susceptible, intermediate, or resistant) were
assigned on the basis of the results of both methods. The result of the
broth microdilution test was considered definitive. The total category
error rate with the Vitek system and the recent clinical isolates (11,902
organism-antimicrobial comparisons) was 4.5%, i.e., 1.7% very major errors,
0.9% major errors, and 1.9% minor errors. The total category error rate
calculated from tests performed with the challenge set (i.e., 8,800
organism-antimicrobial comparisons) was 5.9%, i.e., 2.2% very major errors,
1.1% major errors, and 2.6% minor errors. Very major error rates higher
than the totals were noted with Enterobacter cloacae versus
ampicillin-sulbactam, aztreonam, ticarcillin, and ticarcillin-clavulanate
and with P. aeruginosa versus mezlocillin, ticarcillin, and
ticarcillin-clavulanate. Major error rates higher than the averages were
observed with Proteus mirabilis versus imipenem and with Klebsiella
pneumoniae versus ofloxacin. Excellent overall interlaboratory
reproducibility was observed with the Vitek system. The importance of
inoculum size as a primary determinant in the accuracy of susceptibility
test results with the Vitek system was clearly demonstrated in this study.
Specifically, when an inoculum density fourfold higher than that
recommended by the manufacturer was used, high rates of false resistance
results were obtained with cell wall-active antimicrobial agents versus
both the Enterobacteriaceae and P. aeruginosa.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Multicenter laboratory evaluation of the bioMerieux Vitek antimicrobial susceptibility testing system with 11 antimicrobial agents versus members of the family Enterobacteriaceae and Pseudomonas aeruginosa
University of Massachusetts Medical Center, Worcester 01655, USA.
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