Effect of increasing inoculum sizes of Aspergillus hyphae on MICs and MFCs of antifungal agents by broth microdilution method.

In order to investigate the influence of different hyphal inoculum sizes on minimal inhibition concentrations (MICs) and minimum fungicidal concentrations (MFCs) of amphotericin B (AMB), voriconazole and itraconazole, five isolates each of Aspergillus fumigatus, Aspergillus flavus, Aspergillus niger and Aspergillus terreus were studied using a broth microdilution method. Three inoculum sizes were used: 1 x 10(3)-5 x 10(3), 1 x 10(4)-5 x 10(4) and 1 x 10(5)-5 x 10(5) cfu/ml. MICs and MFCs were read at 24 and 48 h at 35 degrees C. For all species tested, AMB MICs and MFCs were minimally affected by inoculum size on. However inoculum size significantly affected MICs and MFCs of voriconazole and itraconazole; there was an increase of up to 6-fold in MICs and MFCs for the various aspergilli when the inoculum increased from 10(3) to 10(5) cfu/ml (P<0.05). Thus azoles showed significant inoculum effects, while AMB showed comparatively minimum inoculum effects against Aspergillus spp.