Evaluation of the MICUR system for quantitative antimicrobial susceptibility testing: a multiphasic comparison with reference methods

Four laboratories participated in a three-phase study to evaluate the MICUR antimicrobial broth microdilution system (Boehringer Mannheim Diagnostics, Inc., Houston, Tex.). The dried-antimicrobial agent MICUR system was compared with a reference broth microdilution method (National Committee for Clinical Laboratory Standards) by using 304 recently isolated clinical strains and two collections of stock or challenge organisms. Of 7,092 minimum inhibitory concentration (MIC) datum pairs derived from the clinical isolates, 96.6% were within an acceptable (+/- 1 log2 dilution) range. MICUR MICs agreed with the reference broth microdilution method MICs in 95.3% of 6,840 MIC pair determinations performed on stock or challenge cultures. The MICUR intralaboratory reproducibility within +/- 1 log2 dilution step for the clinical isolates was 98.4%. The MICUR intralaboratory and interlaboratory reproducibilities for 26 stock cultures were 98.4 and 95.1%, respectively. For 180 challenge cultures (4,199 MIC pairs) which were included in the MICUR testing to provide a wide variety of antimicrobial susceptibility and resistance patterns, the results for 92.5% were in close agreement with the reference broth microdilution results. No specific resistance mechanism went unrecognized by this new commercial system. The MICUR system gives comparable MIC results when evaluated against the reference broth microdilution method, and it would be acceptable for use in clinical microbiology laboratories.