Phylogenetic Insights into Antifungal Susceptibility: Comparing Environmental and Clinical Scedosporium and Lomentospora Isolates from Taiwan

ObjectivesScedosporium and Lomentospora species are intrinsically resistant molds increasingly implicated in invasive infections with poor outcomes. Olorofim, a novel orotomide antifungal, has demonstrated potent activity against various molds. This study evaluated the antifungal susceptibility of clinical and environmental isolates, focusing on olorofim, and examined these data in a phylogenetic context. MethodsA total of 216 isolates (Scedosporium spp., n=205; L. prolificans, n=11) were collected from clinical and environmental sources across Taiwan. Species identification was confirmed by sequencing of the ITS and {beta}-tubulin regions, followed by maximum-likelihood phylogenetic analysis. Antifungal susceptibility was determined using CLSI M38-A3 method. Cross-resistance was evaluated using correlation analyses. Phylogenetic signal, Mantel tests, and variance partitioning were applied to assess the evolutionary structuring of minimum inhibitory concentrations (MICs). ResultsScedosporium apiospermum (46.3%) and S. boydii (15.7%) were the predominant species, exhibiting comparable triazole susceptibility profiles (MIC90: voriconazole 1-2 mg/L, posaconazole 4 mg/L, and isavuconazole 8 mg/L). L. prolificans displayed pan-resistance to all agents except olorofim. Among triazoles, voriconazole yielded the lowest MICs for most Scedosporium isolates. Olorofim exhibited the lowest MICs across Scedosporium spp. and L. prolificans (all MIC90 [≤]0.12 mg/L). Rare taxa (S. marinum, S. haikouense, S. multisporum, S. minutisporum, S. sp. nov.1) were also identified, exhibiting variable triazole MICs but consistently low olorofim MICs. The association between antifungal susceptibility and species relatedness varied by drug: moderate for posaconazole, amphotericin B, and voriconazole; intermediate for olorofim; weak for isavuconazole; and absent for itraconazole. Most MIC variability (72.5-89.2%) occurred within rather than between species. ConclusionsAntifungal susceptibility among Scedosporium spp. and L. prolificans was drug dependent. Olorofim demonstrated consistently low MICs across species, whereas amphotericin B and triazoles showed variable, species-specific activity. These findings highlight olorofim as a promising therapeutic option and emphasize the need for target gene-based investigations to elucidate the evolutionary basis of antifungal resistance.