Antifungal Susceptibility ofCandidaBiofilms: Unique Efficacy of Amphotericin B Lipid Formulations and Echinocandins

Abstract

ABSTRACTBiofilms, likely the predominant mode of device-related microbial infection, exhibit resistance to antimicrobial agents. Evidence suggests thatCandidabiofilms have dramatically reduced susceptibility to antifungal drugs. We examined antifungal susceptibilities ofCandida albicansandCandida parapsilosisbiofilms grown on a bioprosthetic model. In addition to conventional agents, we determined if new antifungal agents (triazoles, amphotericin B lipid formulations, and echinocandins) have activities againstCandidabiofilms. We also explored effects of preincubation ofC. albicanscells with subinhibitory concentrations (sub-MICs) of drugs to see if they could modify subsequent biofilm formation. Finally, we used confocal scanning laser microscopy (CSLM) to image planktonic- and biofilm-exposed blastospores to examine drug effects on cell structure.Candidabiofilms were formed on silicone elastomer and quantified by tetrazolium and dry weight (DW) assays. Susceptibility testing of fluconazole, nystatin, chlorhexidine, terbenafine, amphotericin B (AMB), and the triazoles voriconazole (VRC) and ravuconazole revealed resistance in allCandidaisolates examined when grown as biofilms, compared to planktonic forms. In contrast, lipid formulations of AMB (liposomal AMB and AMB lipid complex [ABLC]) and echinocandins (caspofungin [Casp] and micafungin) showed activity againstCandidabiofilms. Preincubation ofC. albicanscells with sub-MIC levels of antifungals decreased the ability of cells to subsequently form biofilm (measured by DW;P< 0.0005). CSLM analysis of planktonic and biofilm-associated blastospores showed treatment with VRC, Casp, and ABLC resulted in morphological alterations, which differed with each agent. In conclusion, our data show thatCandidabiofilms show unique susceptibilities to echinocandins and AMB lipid formulations.