Rapid detection of anidulafungin and fluconazole susceptibility profiles of clinical Candida strains by MALDI-TOF MS

Invasive fungal infections caused by resistant Candida species are a global public health problem. Increasing antifungal resistance makes antifungal susceptibility tests (AFST) crucial, necessitating rapid methods. This study aims to determine the fluconazole and anidulafungin susceptibility profiles of clinical Candida strains using matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and compare the results with the European Committee on Antimicrobial Susceptibility Testing (EUCAST) reference broth microdilution method to assess the accuracy and reproducibility of MALDI-TOF MS in evaluating in vitro antifungal susceptibility. The susceptibilities of 40 Candida glabrata isolates for anidulafungin and fluconazole, and 40 Candida albicans and 40 Candida parapsilosis isolates for fluconazole were tested. Candida isolates were incubated for 3 h at two different antifungal concentrations ("maximum" and "breakpoint" concentrations) and a drug-free control (Anidulafungin: 16, 0.06, and 0 mg L-1; Fluconazole: 256, 16, and 0 mg L-1). MALDI-TOF MS spectra from these concentrations were used to create composite correlation index (CCI) matrices for each isolate. The strains with the "mean CCI of the breakpoint/maximum concentration" of which was higher than the "mean CCI of the breakpoint/null concentration" were classified as susceptible. Classifications defined by the MS-AFST method were compared to those based on the EUCAST broth microdilution method. The overall agreement between MS-AFST and EUCAST AFST ranged from 60% to 85%, highest for C. glabrata and anidulafungin. The reproducibility of the MS-AFST assay ranged from 45% to 75%, highest for C. parapsilosis and fluconazole. The study suggests that the MALDI-TOF MS method for assessing antifungal susceptibility in Candida strains is promising but requires further improvements for enhancing the accuracy and reproducibility.