A simplified MALDI-TOF MS method for rapid fluconazole susceptibility testing in Candida species

Introduction. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is widely used for rapid micro-organism identification and has recently been explored for antifungal susceptibility testing (AFST). Hypothesis. Although MALDI-TOF MS has emerged as a promising tool for AFST, simplified and clinically applicable strategies for rapid fluconazole (FLZ) susceptibility detection in Candida spp. remain insufficiently validated. We hypothesized that a streamlined AFST-MS approach would demonstrate good categorical agreement (CA) with the European Committee on Antimicrobial Susceptibility Testing (EUCAST) reference method while significantly reducing turnaround time. Aim. To establish a simplified MALDI-TOF MS-based AFST approach for detecting FLZ resistance in Candida species. Methodology. Fifty-one clinical isolates and reference strains were incubated for 3 h in the presence of FLZ at two concentrations (32 and 4 µg ml −1 ) and in drug-free controls. Spectral profiles were compared with the EUCAST reference method. Results. Overall CA between AFST-MS and EUCAST was 85.2% (κ=0.7306). Species-specific accuracy was 100% for Candida auris, Pichia kudriavzevii (formerly Candida krusei ), Candida tropicalis and Candida parapsilosis ; 92.9% for Candida albicans and 40% for Nakaseomyces glabrata (formerly Candida glabrata ); however, these estimates should be interpreted cautiously given the limited number of isolates per species. All discrepancies were minor errors, with no major or very major errors observed. The method reduced analysis time from 24 to 3 h and enabled presumptive FLZ susceptibility detection with good overall agreement with the reference method Conclusion. These findings support the potential of MALDI-TOF MS as a rapid adjunct tool for antifungal susceptibility assessment and may contribute to earlier therapeutic decision-making.