Evaluation of etest for direct antifungal susceptibility testing of yeastsin positive blood cultures

The performance of the Etest (AB BIODISK, Solna, Sweden) for direct antifun gal susceptibility testing of yeasts in positive blood cultures was compare d with that of the macrodilution method for determining the MICs of five an tifungal agents. Culture broths with blood from bottles positive for yeasts were inoculated directly onto plates for susceptibility testing with the E test, and the MICs were read after 24 and 48 h of incubation, A total of 14 1 positive blood cultures (72 cultures of Candida albicans, 31 of Candida t ropicalis, 14 of Candida glabrata, 11 of Candida parapsilosis, 3 of Candida krusei, and 3 of Cryptococcus neoformans, 3 miscellaneous yeast species, a nd 3 mixed cultures) were tested, and the rates of MIC agreement (+/- log(2 ) dilution) between the direct Etest (at 24 and 48 h, respectively) and mac rodilution methods were as follows: amphotericin B, 81.8 and 93.5%; flucyto sine, 84.8 and 87.7%; fluconazole, 89.4 and 85.5%; itraconazole, 69.7 and 6 3.8%; ketoconazole, 87.9 and 79.0%. By a large-sample t test, the differenc e in log, dilution between the direct Etest and the macrodilution method wa s found to be small (P < 0.05), The lone exceptions were ketoconazole at 18 h of incubation and itraconazole at both 23 and 48 h of incubation (P > 0, 05), By Tukey's multiple comparisons, the difference between the direct Ete st (48 h) and reference methods among different species was found to be les s than I log, dilution. When the MICs were translated into interpretive sus ceptibility, the minor errors caused by the direct Etest (at 24 and 48 h, r espectively) were as follows: flucytosine, 2.3 and 1.4%: fluconazole, 3.0 a nd 3.6%; itraconazole, 21.2 and 21.3%. Itraconazole also produced an additi onal 3.0 and 3.6% major errors as determined by the direct Etest at 24 and 48 h, respectively. It was concluded that, except for itraconazole, the Ete st method was feasible for direct susceptibility testing of blood cultures positive for yeasts, The method is simple, and the results could be read be tween 24 and 48 h after direct inoculation, whenever the inhibition zones w ere discernible.