Quality Control and Reference Guidelines for CLSI Broth Microdilution Method (M38-A Document) for Susceptibility Testing of Anidulafungin against Molds

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Abstract
The CLSI (formerly NCCLS) M38-A document for antifungal susceptibility testing of filamentous fungi does not describe guidelines for echinocandins. A multicenter study (eight centers) evaluated inter- and intralaboratory reproducibilities of two reading times (24 and 48 h or 48 and 72 h) and two end points (MICs and minimum effective concentrations [MECs]) for evaluating anidulafungin against molds. Anidulafungin MICs (≥50% inhibition) and MECs (morphological hyphal changes) were determined for seven Aspergillus isolates (four species) and one isolate each of Fusarium moniliforme , Fusarium solani , and Paecilomyces variotii and for two Scedosporium apiospermum isolates. The inter- and intralaboratory reproducibilities of 10 replicate tests performed in each laboratory on 10 different days for each isolate was 100% at 24 h (MECs, ≤0.015 μg/ml) for six Aspergillus and P. variotii isolates. The reproducibility was 94 to 96.7% at 72 h (MECs, 1 to 8 μg/ml) for S. apiospermum and 96.7 to 97.5% at 48 h (MICs, ≥32 μg/ml) for both Fusarium isolates. Introduction of these identified optimum testing conditions for anidulafungin into future versions of the M38 document is warranted.