Performance of the Sensititre YeastOne assay compared with EUCAST E.Def 9.4 against Fusarium clinical isolates: focus on voriconazole and amphotericin B

Objectives Despite the global emergence of Fusarium infections, data validating commercial antifungal susceptibility testing against these moulds remain scarce. We evaluated the performance and optimal reading time of the Sensititre YeastOne (SYO) assay against Fusarium clinical isolates compared with the EUCAST reference method. Methods This two-centre study (2011–2023) analysed 123 Fusarium isolates identified via two-step molecular sequencing. In vitro susceptibilities to voriconazole and amphotericin B were evaluated using SYO (24 h and 48 h readouts) versus the EUCAST E.Def 9.4 broth microdilution reference method (48 h readout). Essential agreement (EA) was defined as a ±2 log2 dilution difference; >90% was acceptable. Results Fusarium solani species complex (FSSC) dominated the cohort (85.3%), predominantly F. keratoplasticum and F. pseudensiforme. EUCAST testing revealed high MIC50/MIC90 values of voriconazole (>16/>16 mg/L) and amphotericin B (2/16 mg/L). While 65% (80/123) of isolates displayed positivity by SYO at 24 h, median spectrophotometric growth was significantly greater at 48 h than at 24 h [0.37 (IQR 0.315–0.403) versus 0.18 (0.151–0.206)]. At 48 h, EA approached acceptability for voriconazole (92.7%) and amphotericin B (89.4%). Voriconazole categorical agreement (CA) among FSSC was 88.6% and reached 96.9% for F. pseudensiforme. For amphotericin B, SYO MICs clustered around 4–8 mg/L, yielding 100% very major error for F. keratoplasticum and F. pseudensiforme but 100% CA for F. falciforme, F. petroliphilum and non-FSSC. Conclusions Voriconazole and amphotericin B susceptibility determined by SYO cannot universally replace reference methods due to failure to detect non-WT to amphotericin B for prevalent species within FSSC. However, alongside accurate species-level molecular identification, SYO provides actionable susceptibility data for validated species-antifungal combinations.