EVALUATION OF ALAMAR COLORIMETRIC BROTH MICRODILUTION SUSCEPTIBILITY TESTING METHOD FOR STAPHYLOCOCCI AND ENTEROCOCCI

We compared the results of the Alamar broth microdilution susceptibili ty testing method with the results of the National Committee for Clini cal Laboratory Standards reference broth microdilution method for 119 gram-positive organisms, The strains were tested for their susceptibil ities to 20 antimicrobial agents, Only appropriate antimicrobial agent s were evaluated for each species of bacteria, Absolute categorical ag reement between the reference method and the test method was 91.5% for enterococci, 99.8% for oxacillin-susceptible staphylococci, and 97.4% for oxacillin-resistant staphylococci. Essential agreement (percent c omplete agreement plus percent minor errors) was >99% for all organism s tested, The results for enterococci showed no ver?; major errors, on e major error with ofloxacin, and numerous minor errors with the quino lones. However, all except one of the minor errors were within +/-1 lo g(2) dilution of the reference result, For staphylococci, only 2 very major errors (one each with chloramphenicol and oxacillin), 1 major er ror (chloramphenicol), and 15 minor errors (multiple drugs) were obser ved. The Alamar colorimetric system was easy to use and the results we re easy to read, It appears to be an acceptable method for antimicrobi al susceptibility testing of staphylococci and enterococci.