Mutation, biofilm formation, and cell wall remodeling contribute to echinocandin resistance of Candidozyma auris

Aim This study systematically elucidates the mechanisms of echinocandin resistance in Candidozyma auris (C. auris), providing insights into potential therapeutic strategies.Methods Echinocandin susceptibility of clinical bloodstream C. auris isolates was determined using E-test, and resistance-associated mutations were identified by Sanger sequencing. Biofilm formation under antifungal stress was assessed by crystal violet staining and the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assays. Changes in cell wall components were analyzed using quantitative fluorescence assays, while expression of cell wall biosynthesis–related genes was evaluated by RT-qPCR. Activation of cell wall integrity (CWI) and calcineurin pathways was examined, and the adjunctive effect of calcineurin inhibitors with anidulafungin (ANI) was assessed using disk diffusion and checkerboard assays.Results Echinocandin resistance in the clinical isolate C. auris 01 was attributed to an S639F mutation in FKS1. ANI treatment-induced cell aggregation and enhanced biofilm formation. It also triggered cell wall remodeling, increasing chitin, mannan, and β-glucan levels, accompanied by upregulation of β-glucan synthase (FKS1, FKS2), chitin synthase (CHS1, CHS3), and mannan synthesis (PMR1, PMT1). Furthermore, ANI activated both CWI and calcineurin pathways, indicating adaptive stress responses. Notably, calcineurin inhibition exhibited an additive effect with ANI.Conclusions These results highlight a multifaceted resistance framework involving structural, signaling, and potential genetic alterations.