In vitro induction of resistance to fluconazole and caspofungin in Candida parapsilosis complex species: Implications for virulence and cross-resistance to other antifungals

This study investigates the effects of progressive exposure to fluconazole (FLC) and caspofungin (CSF) on resistance development and virulence traits in the Candida parapsilosis complex. Seventeen isolates (6 C. parapsilosis sensu stricto, 6 C. orthopsilosis, and 5 C. metapsilosis) were exposed to increasing concentrations of FLC and CSF, and minimum inhibitory concentrations (MICs) were determined pre- and post-exposure. Significant increases in MICs for FLC and CSF were observed. Notably, induced resistance to one antifungal agent influenced susceptibility to other antifungals, with an inverse relationship between the MICs of azoles (FLC, itraconazole, and voriconazole) and echinocandins (CSF, anidulafungin, and micafungin). Additionally, there was a significant increase in amphotericin B MICs in samples with induced resistance to both FLC and CSF. Resistance phenotypes remained largely stable after subculturing in antifungal-free media. Antifungal exposure enhanced biofilm formation but did not significantly affect the secretion of key hydrolytic enzymes (esterase, phospholipase, protease, and haemolysin). In vivo virulence remained unchanged post-resistance induction, as assessed using the Galleria mellonella model. Our findings highlight the adaptability of C. parapsilosis complex species to antifungal pressure, underscoring the need for continuous surveillance and the development of novel therapeutic strategies to manage infections caused by these pathogens. The increase in biofilm formation following antifungal exposure presents additional challenges for infection management.