Comparison of Neo-Sensitabs Tablet Diffusion Assay with CLSI Broth Microdilution M38-A and Disk Diffusion Methods for Testing Susceptibility of Filamentous Fungi with Amphotericin B, Caspofungin, Itraconazole, Posaconazole, and Voriconazole

We compared the Neo-Sensitabs tablet assay to both reference M38-A broth microdilution and disk diffusion methods for testing the susceptibility of 183 filamentous isolates to amphotericin B, caspofungin, itraconazole, posaconazole, and voriconazole. Neo-Sensitabs and disk assay inhibition zone diameters, in millimeters, were obtained on nonsupplemented Mueller-Hinton agar at 16 to 48 h. The reproducibility of zone diameters (i.e., the percentage of replicate zone diameters that were within 2 standard deviations of the means), their correlation with either MICs or minimum effective concentrations (for caspofungin only), and the categorical agreement were similar between tablet and disk assays (93 to 100% [R, >0.70] and 79 to 96%, respectively) with four of the five agents. The exceptions were the results for posaconazole tablets (R, 0.686; disk, 0.757; 84% categorical agreement for tablet and 96% for disk). These data suggest the potential value of the Neo-Sensitabs assay for testing 5-microg caspofungin and 1-microg voriconazole posaconazole tablets against all mold isolates, 8-microg itraconazole and 5-microg tablets against all mold isolates except zygomycetes, and 10-microg amphotericin B tablets against zygomycete isolates only.