Iron modulation drives biofilm formation and virulence enzyme production in emerging clinical Candida species: implications for diagnostics and therapeutics

Background The changing epidemiology of candidemia indicates a rise in non-albicans Candida species, especially resistant Candida auris and emerging Candida utilis . Although iron impacts fungal virulence, its role in these species remains poorly understood. This study investigates how manipulating iron levels influences biofilm formation, virulence enzymes, and antifungal susceptibility in clinical isolates. Methods A total of 216 isolates of Candida utilis , Candida albicans , and Candida auris from bloodstream infections over two years were identified via phenotypic methods, MALDI-TOF MS, VITEK 2, and 18S rRNA PCR. Susceptibility was tested using disc diffusion and broth microdilution with ferrous sulphate (FeSO 4 ). Virulence enzyme activities and biofilm formation were assessed under iron-rich and control conditions. Results Candida auris showed multidrug resistance, especially to fluconazole and caspofungin, with iron increasing caspofungin MICs up to 16-fold. Candida utilis exhibited strong biofilm formation and increased phospholipase and proteinase activities in the presence of FeSO 4 , and also showed 4- to 32-fold increases in fluconazole resistance. Biofilm biomass was unaffected by iron, but enzyme activities varied by species and enzyme. Candida albicans had high proteinase and haemolysin activity but responded minimally to iron. Conclusions Iron differentially influences virulence−associated traits (biofilm−related enzyme activities) and antifungal resistance across these Candida species. C. utilis exhibits iron−responsive increases in phospholipase and proteinase activities together with amplified azole resistance, while C. auris shows iron−linked enhancement of echinocandin resistance and sustained expression of key virulence−associated enzymes. These results underscore the importance of accounting for host iron levels and species-specific responses when managing candidemia and indicate the potential for therapies targeting iron.