Background. The NCCLS tests for moulds (M38-P document) are time-consuming and cumbersome and may not be the best methods for evaluating agents with different activity mechanisms. It has been demonstrated that minimum effective concentrations (MECs, morphologic changes) of the new echinocandin, caspofungin, correlate with its in vivo activity and that the Etest is an alternative method for testing other agents against yeasts and moulds. Methods. This study compared caspofungin Etest MICs to MECs and NCCLS MICs, which were determined simultaneously for 167 Aspergillus flavus, A. fumigatus, A. nidulans, A. niger, and A. terreus. Etest MICs were determined on 1.5% RPMI-1640 (RPMI) agar with 2% dextrose at 24 and 48 h. MECs and NCCLS MICs were obtained by using standard RPMI, antibiotic medium 3 (M-3) and two inoculum sizes (10 and 10 CFU/ml). MECs and NCCLS MICs were the lowest drug concentrations that showed approx. >50% inhibition and visual and microscopic changes, respectively, at 24 (MECs and NCCLS MICs) and 48 h (NCCLS MICs). Results. The agreement (% of pairs within a 3-dilution range) was species/parameter dependent. The highest overall agreement (93%) was between 48 h Etest MICs and MECs with M-3 and the higher inoculum; the lowest (4.7-5%) between 24 h Etest MICs and both MECs and NCCLS MICs with RPMI and the higher inoculum. The agreement was lower for A. terreus (overall agreement: 91-93% versus 94 -98% for the other four species). Results were more comparable between Etest and MEC pairs (89-93%) than between Etest and NCCLS MICs (86-90%); similar superior results were observed with the higher inoculum. Conclusion. The potential utility of the Etest method as a convenient alternative for the susceptibility testing of Aspergillus spp. is suggested. The clinical value of these results should be determined in clinical trials.
Full conference title:
- ICAAC 41st