The "dip effect" phenomenon complicates antifungal susceptibility testing with gradient concentration strips. Of 60 Candida isolates tested with the three echinocandins, this phenomenon was observed only for caspofungin with most (>90%) Candida albicans, Candida glabrata, and Candida tropicalis isolates and for isolates with CLSI MICs of ≤0.25 mg/liter. In order to facilitate MIC determination, a practical approach was developed using the inhibition zones at 32, 8, 2, and 1 mg/liter, increasing the agreement with the CLSI method >86%.
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