The antifungal properties of chicken egg cystatin against Candida yeast isolates showing different levels of azole resistance

摘要

The increasing incidence of fungal infections together with the emergence of strains resistant to currently available antifungal drugs calls for the development of new classes of antimycotics. Naturally occurring antifungal proteins and peptides are of interest because of low toxicity, immunornodulatory potential and mechanisms of action distinct from those of currently available drugs. In this study, the potent antifungal activity of cystatin, affinity-purified from chicken egg white (CEWC), against the most frequent human fungal pathogens of the genus Candida was identified and characterised. CEWC inhibited the growth of azole-sensitive Candida albicans isolates with minimal inhibitory concentration (MIC) values ranging from 0.8 to 3.3 mumol l~(-1), a potency comparable with those of fluconazole and histatin 5, the antimicrobial peptide of the human saliva. Similarly to histatin 5, CEWC activity was not compromised in azole-resistant isolates overproducing the multidrug efflux transporters Cdr1p and Cdr2p and did not antagonise fluconazole or amphotericin B. CEWC had candidacidal activity, as revealed by the time-kill assay, and, similarly to histatin 5, completely inhibited the growth at supra-MIC concentrations. This was in contrast to the fungistatic effect and trailing growth observed with fluconazole. CEWC inhibited the growth of Candida parapsilosis and Candida tropicalis at similar concentrations, whereas Candida glabrata was more resistant to CEWC.