© 2002 The British Society for Antimicrobial Chemotherapy In vitro susceptibilities of zygomycetes to conventional and new antifungals

In vitro susceptibilities of 36 zygomycete isolates, belonging to six genera, to itraconazole, posaconazole, voriconazole, terbinafine, amphotericin B and 5-fluorocytosine were determined by using a broth microdilution adaptation of the National Committee for Clinical Laboratory Standards M-38P reference method. The influence of incubation time on MIC values, and the per-formance of a spectrophotometric method for MIC determination in comparison with the visual reference method, were also evaluated. Amphotericin B was active against most of the isolates. All the isolates were highly resistant to 5-fluorocytosine (MICs> 256 mg/L). Voriconazole was significantly less active than the other drugs with an overall MIC90 (MIC at which 90 % of the isolates were inhibited) of 32 mg/L. In contrast, posaconazole showed good activity (MIC90 1 mg/L). A wide range of MICs, from 0.03 to ≥32 mg/L, was obtained for itraconazole and terbinafine. Differences in susceptibility between and within genera were noted. Rhizopus spp. were signifi-cantly less susceptible to itraconazole, posaconazole, terbinafine and amphotericin B than Absidia spp., and less susceptible than Mucor spp. to amphotericin B. Terbinafine appeared to be more active against Rhizopus microsporus than against Rhizopus oryzae (geometric mea