Efficacy of micro dilution method for testing susceptibility to azole antifungal agents using a semisolid medium (Synthetic amino acid medium, fungal)

We evaluated the efficacy of a susceptibility testing method for azole antifungal agents (miconazole, fluconazole, itraconazole) using a semisolid medium [synthetic amino acid medium, fungal (SAAMF), pH 7.4, plus 0.25% agar noble (Difco)] in 96 well plates. Minimal inhibitory concentrations (MICs) were measured after incubation at 30°C for 48 hours. Seventy-four strains clinically isolated 1989—1990 at Nagasaki University Hospital were tested in this study, with the following results. 1)Correlation between MICs determined in semisolid SAAMF and 99% inhibitory concentration (IC₉₉): good correlation was seen between the MIC method and IC₉₉in miconazole and fluconazole, their correlation coefficients being 0.95 and 0.93. But the correlation in itraconazole was poor, particularly in Candida albicans. In this strain, 24 h incubation was rather favorable. 2)Antifungal activity against clinical isolates: miconazole had excellent activity against Candida albicans and Candida glabrata. Itraconazole showed superior activity against Candida tropicalis, Candida parapsilosis, Candida krusei and Cryptococcm neoformans. 3)Visual determination of endpoints: so-called trailing endpoints were seen, but they were generally weak. Hence it was not difficult to determine the endpoints. 4)Efficacy of the MIC method: firstly, the MICs could be determined visually. Secondly, the method was so efficient that six isolates could be tested on one plate. Thirdly, it was economical because only very small quantities of media and reagents were required.