EVALUATION OF THE DADE MICROSCAN MICROSTREP ANTIMICROBIAL SUSCEPTIBILITY TESTING PANEL WITH SELECTED STREPTOCOCCUS-PNEUMONIAE CHALLENGE STRAINS AND RECENT CLINICAL ISOLATES

The MicroScan MICroSTREP panel is a recently marketed frozen broth mic rodilution panel for susceptibility testing of various streptococci, i ncluding Streptococcus pneumoniae, The panel contains 10 antimicrobial agents in cation-adjusted Mueller-Hinton broth supplemented with 3% l ysed horse blood, similar in concept to the National Committee for Cli nical Laboratory Standards (NCCLS) reference broth microdilution metho d for testing streptococci. A group of 210 isolates of S. pneumoniae w ere selected to include isolates with previously documented resistance to agents incorporated in the MICroSTREP panel, as well as recent inv asive clinical isolates, All isolates were tested simultaneously with the MICroSTREP panel and an NCCLS reference panel whose drug concentra tions were prepared to coincide,vith those of the MICroSTREP panel, Of the 210 isolates, 5 failed to grow in the MICroSTREP panel; 3 of thos e also did not grow in the reference panel. Essential agreement of MIC s determined by the two methods (test MIC +/- one dilution of the refe rence MIG) was 99.6% overall and ranged from 98.0% with chloramphenico l to 100%,vith penicillin, ceftriaxone, erythromycin, tetracycline, an d vancomycin, There were no very major or major interpretive category errors resulting from the MICroSTREP panel tests, Minor interpretive c ategory errors ranged from 12.2% with cefotaxime and 9.8% with ceftria xone (due mainly to clustering of MICs for the selected strains near t he breakpoints) to 0% with chloramphenicol and vancomycin, These resul ts indicate that the MicroScan MICroSTREP frozen panels provide suscep tibility results with pneumococci that are essentially equivalent to r esults derived by the NCCLS reference broth microdilution procedure.