COMPARISON OF VISUAL AND SPECTROPHOTOMETRIC METHODS OF MIC END-POINT DETERMINATIONS BY USING BROTH MICRODILUTION METHODS TO TEST 5 ANTIFUNGAL AGENTS, INCLUDING THE NEW TRIAZOLE-D0870

A study to compare three different methods for reading MIC endpoints t ested by the broth microdilution modification of the National Committe e for Clinical Laboratory Standards (Villanova, Pa.) reference method was conducted, MICs of amphotericin B, flucytosine, fluconazole, itrac onazole, and a new triazole, D0870, were determined for five reference yeast strains and 100 clinical isolates of Candida spp. MICs were rea d visually according to National Committee for Clinical Laboratory Sta ndards guidelines from microdilution trays that had been (VS) and had not been (V) shaken. MICs were also determined spectrophotometrically (SP) at 492 nm, SP endpoints were determined as the concentrations res ulting in a greater than or equal to 50% inhibition of growth (flucyto sine and azoles) and a greater than or equal to 90% inhibition of grow th (amphotericin B) relative to control growth. The five reference str ains were tested nine times each against all five antifungal agents, a nd the MIC results for each reading method were compared with a 3-log( 2) dilution reference range determined by the macrodilution (M27-P) me thod. Overall, 84 to 100% of the MICs determined by V, 93 to 100% of t hose determined by VS, and 89 to 100% of those determined by SP fell w ithin the 3-log(2) dilution reference range for each reference strain and antifungal agent. Reproducibility was 99% for V and SP and 98% for VS. Agreement among the three methods of reading ranged from 97 to 99 %. Excellent agreement among reading methods was also observed for all antifungal agents when tested against 100 clinical isolates, Agreemen t between the standard V method (no agitation) and VS ranged from 99 t o 100%, and that between V and SP ranged from 89 to 99%. The VS and SP reading methods provided more definitive endpoints than the V method, which does not involve shaking.