AAC Accepts, published online ahead of print on 14 July 2008

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Antimicrob. Agents Chemother. doi:10.1128/AAC.00541-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Cell Density and Cell Ageing as Factors Modulating Antifungal Resistance of Candida albicans Biofilms

C. J. Seneviratne, L. J. Jin, Y. H. Samaranayake, and L. P. Samaranayake^*

Oral BioSciences, Faculty of Dentistry; The University of Hong Kong, Hong Kong

^* To whom correspondence should be addressed. Email: lakshman{at}hku.hk.

Biofilm formation is a major virulence attribute of Candida pathogenicity which contributes to higher antifungal resistance. We investigated the role of cell density and cellular ageing on the relative antifungal susceptibility of planktonic, biofilm and, biofilm derived planktonic modes of Candida. A reference and a wild type strain of C. albicans were used to evaluate MIC of caspofungin (CAS), amphotericin B (AMB), nystatin (NYT), ketoconazole (KTC) and flucytosine (5FC). Standard, NCCLS and EUCAST methods were used for planktonic MIC determination. 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 sizes and, 24 and 48 h old cultures of planktonic Candida. Furthermore, Candida biofilm derived planktonic cells (BDPC) were also subjected to antifungal susceptibility testing. Both C. albicans strains, in the planktonic mode showed low MICs although on increasing the inoculum size (up to 1x 10⁸ cells/ml) a variable MIC was noted. On the contrary, Candida biofilms showed 15 to > 1,000 fold higher MIC to antifungals. Interestingly; BDPC showed lower MIC values that were similar to planktonic mode particularly for CAS and AMB. Our data indicate that higher antifungal resistance of Candida biofilms is an intrinsic feature possibly related to the biofilm architecture, rather than the cellular density or cellular aging.

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