Evaluation of antifungal susceptibility profiles of clinical candida and aspergillus strains by matrix assisted laser desorption/ionization time-of-FLİGHT MASS spectrometry ("MALDİ-TOF MS") method

Invasive fungal infections caused by resistant Candida and Aspergillus species are a global public health problem. Considering the increasing resistance to antifungals, antifungal susceptibility tests (AFST) are becoming increasingly important, and rapid methods are needed. The aim of this study is to determine the azole and echinocandin susceptibilities of clinical Candida and Aspergillus strains isolated at Hacettepe University Faculty of Medicine Medical Mycology Laboratory by using MALDI-TOF MS and compare the results with those obtained by the EUCAST reference broth microdilution method for assessment of the accuracy and reproducibility of MALDI-TOF MS for evaluation of in vitro antifungal susceptibility. In this study, the susceptibilities of 40 Candida glabrata isolates for anidulafungin and fluconazole, 40 Candida albicans and 40 Candida parapsilosis isolates for fluconazole and 4 Aspergillus fumigatus isolates for voriconazole were tested. Candida isolates were incubated for 3 hours at two different antifungal concentrations as "maximum" and "breakpoint" and in the drug-free control (Anidulafungin: 16, 0.06, 0 mg/L; Fluconazole: 256, 16, 0 mg/L). A. fumigatus isolates were incubated at serial voriconazole concentrations (32-0.03 mg/L) and in the drug-free control for 15 hours. The MALDI-TOF MS spectra obtained from these concentrations were used to create the composite correlation index (CCI) matrices for each isolate. For Candida species, the strains whose "mean CCI of the breakpoint/maximum concentration" was higher than the "mean CCI of the breakpoint/null concentration" were classified as susceptible. For A. fumigatus, the lowest drug concentration at which the spectrum was more similar to the one observed at the maximum drug concentration than that in the drug-free control was defined as the minimum profile changing concentration (MPCC). Classifications defined by the MS-AFST method were compared with categorizations of susceptible or resistant based on the EUCAST broth microdilution method. Overall, the agreement between MS-AFST and EUCAST AFST ranged from 60% to 85%, with the highest percentage in the C. glabrata and anidulafungin group. The reproducibility of the MS-AFST assay ranged from 45% to 75% and is best for C. parapsilosis and fluconazole group. Full agreement and reproducibility were observed for four A. fumigatus strains. In conclusion, the MALDI-TOF MS method can be used simultaneously for both identification and antifungal susceptibility categorization in Candida and Aspergillus species if further studies are conducted to improve the methodology and the reproducibility of the test.