Comparative evaluation of a new commercial colorimetric microdilution assay (SensiQuattro Candida EU) with MIC test strip and EUCAST broth microdilution methods for susceptibility testing of invasive Candida isolates

Candidemia is an important cause of morbidity and mortality in immunosuppressed patients. Candida isolates must be cultivated, identified, and tested for susceptibility. We compared the performance of a new colorimetric broth microdilution panel (SensiQuattro Candida EU) for antifungal susceptibility testing to that of Liofilchem's MIC test strip and the EUCAST reference broth microdilution protocol. We tested 187 blood culture isolates of 5 Candida spp. (120 C. albicans, 38 C. glabrata, 10 C. parapsilosis, 12 C. tropicalis, and 7 C. krusei) against seven antifungal agents (amphotericin B, fluconazole, voriconazole, posaconazole, caspofungin, anidulafungin, and micafungin) and interpreted the MICs according to the EUCAST recommendations. If applicable, the overall essential agreement (EA) of the SensiQuattro panel with the reference broth microdilution was slightly higher for C. albicans (87%) than for other species (85.8%). We found that SensiQuattro performed best in testing amphotericin B (EA, 100%), voriconazole (EA, 93.7%), and posaconazole (EA, 94.8%) against C. albicans, but its error rate for this species was high (29.6%) because of mainly major errors (26.7%) in testing anidulafungin and micafungin. Compared to the SensiQuattro panel, the MIC test strip exhibited a higher level of agreement for most isolates. SensiQuattro assays are easy to perform, but they are currently not suitable for testing echinocandins against Candida spp.