Comparison of the colorimetric microdilution-based commercial MICRONAUT-AM test with the conventional broth microdilution test in assessing antifungal susceptibility of multidrug-resistant Candidozyma (Candida) auris

Aims: Candidozyma (Candida) auris is a pathogen that causes invasive infections and develops multidrug resistance. Antifungal susceptibility testing is vital for therapeutic management. In this context, this study was conducted to compare the efficacies of the commercial MICRONAUT-AM test (MN) and the conventional broth microdilution test (BMD) in assessing antifungal susceptibility of C. auris isolates. Methods: The material of this comparative study consisted of 116 C. auris strains isolated between February 2024 and April 2024. The efficacies of MN and BMD in assessing the susceptibility of C. auris isolates to antifungal agents, including fluconazole, amphotericin B, micafungin, and anidulafungin, were compared. To this end, the agreement and essential agreement between the two tests and minor, major, and very major error rates were calculated. Results: The agreement between the two tests was found to be high (98.3%) in assessing the susceptibility of C. auris isolates to micafungin and anidulafungin agents but low in assessing their susceptibility to fluconazole and amphotericin B agents. C. auris isolates were found to be 66.4% resistant to fluconazole with BMD and 94.8% resistant with MN, while they were found to be 44% resistant to amphotericin B with BMD and not resistant with MN. Compared to the reference method BMD, the MN detected the resistance of C. auris isolates against micafungin and anidulafungin agents with high accuracy but could not accurately detect their resistance against fluconazole and amphotericin B agents. Conclusion: Our findings suggest that the commercial test kit evaluated in this study may require optimization with respect to the antifungal agents it includes. Confirmation of these results through comparative studies involving different commercial kits is necessary to determine whether similar findings can be observed.