Addition of DNase improves the in vitro activity of antifungal drugs against Candida albicans biofilms

Cells within Candida albicans biofilms display decreased susceptibility to most clinically used antifungal agents. We recently demonstrated that extracellular DNA (eDNA) plays an important role in biofilm integrity, as a component of the biofilm matrix. This study aimed at gaining insights into the contributions of eDNA to C. albicans biofilms antifungal susceptibility by the investigation of the impact of the combined use of deoxyribonuclease I (DNase) and antifungals to treat biofilms. Candida albicans biofilms were formed using a simple and reproducible 96-well plate-based method. The activity of the combined use of 0.13 mg l(-1) DNase and antifungals was estimated using the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT) reduction assay and total viable counts. Herein, we report the improved efficacy of amphotericin B when in combination with DNase against C. albicans biofilms, as assessed using XTT readings and viable counts. Furthermore, although DNase increased the efficacy of caspofungin in the reduction of mitochondrial activity, no changes were observed in terms of culturable cells. Deoxyribonuclease I did not affect biofilm cells susceptibility to fluconazole. This work suggests that agents that target processes affecting the biofilm structural integrity may have potential use as adjuvants of a catheter-lock therapy.This work was supported by the National Institute of Dental & Craniofacial Research (NIDCR) (grant number 5R21DE017294 to J. L.-R.); and National Institute of Allergy and Infectious Diseases (NIAID) (grant number R21AI080930). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIDCR, the NIAID or the National Institutes of Health. The authors thank Merck Sharp & Dohme Portugal for providing part of the caspofungin used in this study. M. M. was financially supported by a fellowship from Fundacao para a Ciencia e Tecnologia, Portugal (contract SFRH/BD/28222/2006), co-financed by the Programa Operacional Potencial Humano (POPH)/Fundo Social Europeu (FSE)