Fluconazole Disk Diffusion on CHROMagar Candida Plus for Differentiation Between Candidozyma auris and Candida parapsilosis

Background: This study evaluated the utility of fluconazole disk diffusion on CHROMagar Candida Plus for differentiating Candidozyma auris from Candida parapsilosis. Methods: In this in vitro study, clinical isolates of both C. auris and C. parapsilosis were used. Antifungal susceptibility testing was performed via broth microdilution and disk diffusion with different fluconazole concentrations on both CHROMagar Candida Plus and RPMI agar. Colony color was also assessed. Results: This study demonstrates high categorical agreement between disk diffusion on CHROMagar Candida Plus and broth microdilution for both species. An optimal cut-off zone diameter of 10 mm was identified on CHROMagar Candida Plus with 50 µg fluconazole, providing 91% sensitivity and 90% specificity for differentiating the two species. Notably, at 24 h, 83 out of 88 (94.3%) C. auris isolates exhibited a bluish, blue-green, or turquoise coloration on the reverse side of the plate, suggesting that reverse-side colony color on CHROMagar may serve as a supportive phenotypic indicator when combined with disk diffusion testing, to differentiate C. auris from C. parapsilosis in the laboratory setting. Conclusions: Fluconazole disk diffusion on CHROMagar Candida Plus, supplemented by reverse-side colony coloration, offers a practical, low-cost adjunctive strategy to aid in the differentiation of C. auris and C. parapsilosis in clinical laboratories.