COMPARISON OF A SPECTROPHOTOMETRIC MICRODILUTION METHOD WITH RPMI-2-PERCENT GLUCOSE WITH THE NATIONAL COMMITTEE FOR CLINICAL LABORATORY STANDARDS REFERENCE MACRODILUTION METHOD M27-P FOR IN-VITRO SUSCEPTIBILITY TESTING OF AMPHOTERICIN-B, FLUCYTOSINE, AND FLUCONAZOLE AGAINST CANDIDA-ALBICANS

The National Committee for Clinical Laboratory Standards has proposed a reference broth macrodilution method for in vitro antifungal suscept ibility testing of yeasts (the M27-P method), This method is cumbersom e and time-consuming and includes MIC endpoint determination by visual and subjective inspection of growth inhibition after 48 h of incubati on. An alternative microdilution procedure was compared with the M27-P method for determination of the amphotericin B, flucytosine, and fluc onazole susceptibilities of 8 American Type Culture Collection strains (6 of them were quality control or reference strains) and 50 clinical isolates of Candida albicans, This microdilution method uses as cultu re medium RPMI 1640 supplemented with 18 g of glucose per liter (RPMI- 2% glucose). Preparation of drugs, basal medium, and inocula was done by following the recommendations of the National Committee for Clinica l Laboratory Standards, The MIC endpoint was calculated objectively fr om the turbidimetric data read at 24 h, Increased growth of C. albican s in RPMI-2% glucose and its spectrophotometric reading allowed for th e rapid (24 h) and objective calculation of MIC endpoints compared wit h previous microdilution methods with standard RPMI 1640, Nevertheless , good agreement was shown between the M27-P method and this microdilu tion test, The MICs obtained for the quality control or reference stra ins by the microdilution method were in the ranges published for those strains, For clinical isolates, the percentages of agreement were 100 % for amphotericin B and fluconazole and 98.1% for flucytosine. These data suggest that this microdilution method may serve as a less subjec tive and more rapid alternative to the M27-P method for antifungal sus ceptibility testing of yeasts.