title: Cell density and cell aging as factors modulating antifungal resistance of Candida albicans biofilms.
abstract: Biofilm formation is a major virulence attribute of Candida pathogenicity which contributes to higher antifungal resistance. We investigated the roles of cell density and cellular aging on the relative antifungal susceptibility of planktonic, biofilm, and biofilm-derived planktonic modes of Candida. A reference and a wild-type strain of Candida albicans were used to evaluate the MICs of caspofungin (CAS), amphotericin B (AMB), nystatin (NYT), ketoconazole (KTC), and flucytosine (5FC). Standard, NCCLS, and European Committee on Antibiotic Susceptibility Testing methods were used for planktonic MIC determination. Candida biofilms were then developed on polystyrene wells, and MICs were determined with a standard 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide assay. Subsequently, antifungal susceptibility testing was performed for greater inoculum concentrations and 24- and 48-h-old cultures of planktonic Candida. Furthermore, Candida biofilm-derived planktonic cells (BDPC) were also subjected to antifungal susceptibility testing. The MICs for both C. albicans strains in the planktonic mode were low, although on increasing the inoculum concentration (up to 1 x 10(8) cells/ml), a variable MIC was noted. On the contrary, for Candida biofilms, the MICs of antifungals were 15- to >1,000-fold higher. Interestingly, the MICs for BDPC were lower and were similar to those for planktonic-mode cells, particularly those of 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 cellular density or cellular aging.
authors.affiliation: Faculty of Dentistry, Oral Biosciences, The University of Hong Kong, Prince Philip Dental Hospital, Hong Kong. lakshman@hku.hk
authors.forename: C J
authors.initials: CJ
authors.lastname: Seneviratne
authors.forename: L J
authors.initials: LJ
authors.lastname: Jin
authors.forename: Y H
authors.initials: YH
authors.lastname: Samaranayake
authors.forename: L P
authors.initials: LP
authors.lastname: Samaranayake
mesh_terms: D000935:Antifungal Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D002176:Candida albicans / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D002448:Cell Adhesion; D015169:Colony Count, Microbial; D003470:Culture Media; D025141:Drug Resistance, Fungal; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D011137:Polystyrenes; D013997:Time Factors
chemical_list: D000935:Antifungal Agents; D003470:Culture Media; D011137:Polystyrenes