Comparison of the minimum fungicidal concentration of amphotericin B determined in filamentous fungi by macrodilution and microdilution methods

Minimum fungicidal concentration (MFC) determination could be useful in sev ere fungal infections in immunocompromised patients. No reference tests to determine the MFC are available, and both macro- and microdilution methods are commonly used. In this study, discrepancies between minimum inhibitory concentrations (MICs) and MFCs of amphotericin B against 58 isolates of fil amentous fungi other than Aspergillus (46 Fusarium spp,, six Paecilomyces s pp. and six Scopulariopsis spp,), obtained with macro- and microdilution me thods, were evaluated, Additionally, the agreement between MFCs obtained by both methods were analysed, In general MFCs were higher than the correspon ding MICs overall using the macrodilution method. MFCs were more than one d ilution higher than MICs in 52.3% of the cases in the macrodilution test an d in 20.5% of the cases in microdilution test. The degree of agreement betw een MFCs obtained with the two methods was of 70.4% (Kappa coefficient of 0 .5). In general, the macrodilution method showed higher MFC values than the microdilution method, Differences of up to six drug dilutions were observe d between MFCs obtained by both methods.