Antifungal susceptibility and in vitro virulence characteristics of clinical Magnusiomyces/Saprochaete isolates: a multicenter study from Türkiye

Abstract Invasive infections due to Magnusiomyces/Saprochaete species are an emerging problem in immunocompromised patients and are often underrecognized because of misidentification and intrinsic resistance to some antifungals. This multicenter study investigated the species distribution, antifungal susceptibility patterns, and key virulence traits of clinical isolates from Türkiye. A total of 133 clinical isolates collected between 2010 and 2024 from 18 hospitals in 10 cities were identified by MALDI-TOF MS and ITS/LSU sequencing. MICs of amphotericin B, fluconazole, voriconazole, itraconazole, posaconazole, and flucytosine were determined using the EUCAST broth microdilution method. Biofilm formation and esterase, caseinase, secreted aspartyl proteinase, phospholipase, and hemolysin activities were assessed phenotypically. Sequencing identified 107 isolates (80.4%) as Magnusiomyces capitatus and 26 (19.6%) as Magnusiomyces clavatus, MALDI-TOF MS identified 106 (79.7%) as M. capitatus and 27 isolates (20.3%) as M. clavatus. There was 99.2% agreement between MALDI-TOF MS and sequencing results. Voriconazole, amphotericin B, and posaconazole showed the lowest MICs, whereas fluconazole displayed wide MIC ranges and limited activity. Overall, 97.7% of isolates were strong biofilm producers, with significantly higher biofilm production in M. capitatus. In contrast, M. clavatus showed higher caseinase and esterase activity. This study provides the most extensive multicenter dataset on Magnusiomyces/Saprochaete in Türkiye and underscores their considerable pathogenic potential through strong biofilm formation and tissue-degrading enzyme activities. Accurate species-level identification using MALDI-TOF MS supported by molecular methods is essential, and limited fluconazole activity suggests that voriconazole and amphotericin B should be prioritized in species-guided treatment strategies.