Abstract
BackgroundBiofilm formation by Candida albicans has shown to be highly variable and is directly associated with pathogenicity and poor clinical outcomes in patients at risk. The aim of this study was to test the hypotheses that the extracellular DNA release by C. albicans is strain dependent and is associated with biofilm heterogeneity.ResultsInitially, biofilm formed by C. albicans high biofilm formers (HBF) or low biofilm formers (LBF) were treated with DNase to find whether eDNA play a role in their biofilm formation. Digestion of biofilm eDNA significantly reduced the HBF biofilm biomass by five fold compared to untreated controls. In addition, quantification of eDNA over the period of biofilm formation by SYBR green assay demonstrate a significantly higher level of 2 to 6 fold in HBF compared to LBF. Biochemical and transcriptional analyses showed that chitinase activity and mRNA levels of chitinase genes, a marker of autolysis, were upregulated in 24 h biofilm formation by HBF compared to LBF, indicating autolysis pathway possibly involved in causing variation. The biofilm biomass and eDNA release by single (∆cht2, ∆cht3) and double knockout (∆cht2/∆cht3) chitinase mutants were significantly less compared to their parental strain CA14, confirming the role of chitinases in eDNA release and biofilm formation. Correlation analysis found a positive correlation between chitinases and HWP1, suggesting eDNA may release during the hyphal growth. Finally, we showed a combinational treatment of biofilms with DNase or chitinase inhibitor (acetazolamide) plus amphotericin B significantly improved antifungal susceptibility by 2 to 8 fold.ConclusionsCollectively, these data show that eDNA release by C. albicans clinical isolates is variable and is associated with differential biofilm formation. Digestion of biofilm eDNA by DNase may provide a novel therapeutic strategies to destabilise biofilm growth and improves antifungal sensitivity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-014-0303-6) contains supplementary material, which is available to authorized users.
Highlights
Biofilm formation by Candida albicans has shown to be highly variable and is directly associated with pathogenicity and poor clinical outcomes in patients at risk
Given that Extracellular DNA (eDNA) contributes to Extracellular matrix (ECM) integrity, and ECM is a key factor in promoting biofilm formation, we hypothesised that the capacity to release eDNA through differential chitinase activity may be an underlying mechanism supporting biofilm heterogeneity
Candida albicans eDNA release is correlated with biofilm formation and promotes antifungal resistance Initially, we assessed C. albicans biofilm formation by six bloodstream isolates defined as either low biofilm former (LBF, n = 3) or high biofilm former (HBF, n = 3) based on biomass quantification
Summary
Biofilm formation by Candida albicans has shown to be highly variable and is directly associated with pathogenicity and poor clinical outcomes in patients at risk. Typical fungal biofilm ECM is a heterogeneous substance consisting of exopolysaccharides, proteins, surfactants, lipids and water [12,13], though recent studies have shown the presence of another important component extracellular DNA in fungal biofilm matrix [13,14] These studies demonstrated that eDNA plays a significant role with respect to structural stability and as a consequence antifungal sensitivity. In both C. albicans and A. fumigatus it was shown that addition of exogenous DNA significantly improved biofilm formation, and that depletion of biofilm eDNA through the addition of DNase adversely affects the biomass [13,14]. Given that eDNA contributes to ECM integrity, and ECM is a key factor in promoting biofilm formation, we hypothesised that the capacity to release eDNA through differential chitinase activity may be an underlying mechanism supporting biofilm heterogeneity
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