A COMPARATIVE-STUDY OF THE BROTH MICRO-DILUTION AND MACRO-DILUTION TECHNIQUES FOR THE DETERMINATION OF THE IN-VITRO SUSCEPTIBILITY OF ASPERGILLUS-FUMIGATUS

The effects of inoculum size, medium, temperature, anti duration of gr owth on the in vitro susceptibility testing of Aspergillus fumigatus w ere investigated using broth micro- and macro-dilution techniques. The minimum inhibitory concentrations (MICs) of ketoconazole, miconazole, itraconazole, fluconazole, and amphotericin B were significantly infl uenced by the inoculum size, regardless of the techniques used. Two- t o four-fold higher MIC values were obtained when the inoculum size was increased 100-fold. The use of peptone yeast extract glucose and RPMI 1640 media provided essentially identical MIC values at 30 and 35 deg rees C after incubation for 48 h or longer. A comparison of broth micr o- and macro-dilution techniques revealed that, under equivalent condi tions, the latter with an inoculum size between 1 x 10(3) and 1 x 10(4 ) conidia (strain W73355)/mL consistently provided the lowest MICs of fluconazole (256 mu g/mL), ketoconazole (8 mu g/mL), miconazole (2 mu g/mL), itraconazole (0.25 mu g/mL), and amphotericin B (0.25 mu g/mL). Using the broth macrodilution technique. we screened 24 clinical isol ates of A. fumigatus obtained from the Detroit Medical Center in 1994. The MIC values of fluconazole, ketoconazole, miconazole, itraconazole and amphotericin B for all the isolates were 128-256, 8-16, 1-2, 0.25 -0.5, and 0.25-1.0 mu g/mL, respectively, indicating that none of the clinical isolates that we tested shows acquired resistance to the anti fungals used.