Antifungal susceptibility of C. albicans and its hyphal mutants

Objectives: Biofilm formation is a major virulence attribute of Candida species which confer higher antifungal resistance to this mode of growth. We investigated the role of transcriptional regulators Efg1 and Cph1 in relation to the antifungal susceptibility of Candida in the planktonic, adhesion and biofilm modes. Methods: A wild type strain of C. albicans and its hyphal mutants were used to evaluate the kinetics and antifungal susceptibility of caspofungin (CAS), amphotericin B (AMB), nystatin (NYT), ketoconazole (KTC) and flucytosine (5FC). Standard CLSI method was used for determination of planktonic MIC. Then, Candida biofilms were developed on polystyrene wells and MIC determined using a standard XTT assay. Subsequently, antifungal susceptibility testing was performed for higher inoculum size (1×10⁷ cells/ml) of planktonic Candida. Furthermore, Candida adhesion phase was also subjected to antifungal susceptibility testing. Results: Compared to planktonic mode, adhesion and biofilm mode of growth were resistant to all the antifungals tested. Fungistatic drugs KTC and 5FC were not effective against high density planktonic cultures, adhesion or biofilm modes of Candida. Although Δ efg/efg1 and ΔΔ cph/cph1 efg/efg1 mutants formed less biofilm than wild type C. albicans SC5314, they were similarly resistant to CAS. However, latter mutants were more sensitive to AMB and NYT. Conclusions: These data indicate that adhesion per se confer fungi a somewhat higher resistance to antifungals which further argument in the biofilm mode. However, the present study also shows that filamentation is not an absolute prerequisite for antifungal resistance in the biofilm mode of Candida.