Antifungal Susceptibility Trends Among Filamentous Fungi: An Epidemiological Evaluation on Aspergillus spp., Fusarium spp., and Scedosporium spp. from Southern Italy

Background/Objectives: Antifungal resistance among filamentous fungi is an increasing global concern with significant implications for clinical management. Herein, we propose a study aiming to investigate in vitro susceptibility patterns and epidemiology of filamentous fungi in Southern Italy, focusing on MIC distributions and resistance trends. Methods: We reported susceptibility results from Aspergillus spp., Fusarium spp., and Scedosporium/Lomentospora spp. clinical isolates, which underwent azoles, echinocandins, and amphotericin B in vitro testing. Results: Aspergillus fumigatus was the most frequently isolated species, showing an alarming increase in reduced susceptibility to amphotericin B (9.1%). The highest MIC ranges for this antifungal drug emerged in the case of A. fumigatus (1-4 mg/L) and A. terreus (2-8 mg/L), while A. flavus (0.5-4 mg/L) and A. niger (0.25-4 mg/L) showed lower values. As regarding azoles, all the Aspergillus spp. strains exhibited variable MIC values, reporting a 0.06-16 mg/L MIC range for itraconazole, 0.125-1 mg/L for voriconazole, and 0.03-1 mg/L for posaconazole. Fusarium solani exhibited high MICs for azoles (8 mg/L) and amphotericin B (2-4 mg/L), while F. oxysporum and F. proliferatum showed lower MICs (0.25-2 mg/L for amphotericin B and a MIC range of 0.5-8 mg/L for posaconazole). Lomentospora prolificans and Scedosporium apiospermum demonstrated multidrug resistance across all tested antifungals, reporting MIC ranges of 4-8 mg/L for amphotericin B, 0.25-16 mg/L for posaconazole, 0.25-8 mg/L for voriconazole, and 0.125-8 for itraconazole. Conclusions: Our data highlight the critical emergence of reduced antifungal susceptibility among filamentous fungi in Southern Italy, underlining the importance of epidemiological surveillance, precise species identification, and optimized susceptibility testing in the case of mould etiology for invasive fungal infections.