Biofilm Growth Characteristics of Candida on Central Venous Catheters

Abstract

C. albicans is frequently isolated from blood stream infections associated with central venous catheters. Objectives: a) To fully characterize the growth and biofilm development of C. albicans on central venous catheter surfaces (CVCs) in YNB medium, b) to determine the expression of upregulated biofilm specific genes encoding adhesins and hyphae in Candida biofilms grown on serum coated/ uncoated catheters and, c) to evaluate the antimycotic efficacy of amphotericin B, azole antifungals and the combination of polyene and azole drugs for the prevention of Candida biofilm growth on catheter surfaces. Methods: Biofilm growth of C. albicans on CVCs in Yeast nitrogen base medium during varying time intervals and growth conditions were determined using the tetrazolium reduction assay. Scanning electron microscopy and Confocal scanning laser microscopy were used to further characterize Candida biofilms. The differential mRNA transcript levels of biofilm associated genes were determined by quantitative real-time PCR analysis.

Results: 1) Biofilm growth was significantly (p<0.001) higher in serum coated CVCs and consisted of yeast and hyphal elements embedded with extracellular material for all C. albicans strains, 2) A significant upregulation of the adhesin genes ALS3, HWP1, EAP1 and the overexpression of ECE1 hyphal gene was observed for clinical C. albicans biofilms (for at least one time point) grown on CVCs in the presence of serum whereas all the above described genes were underexpressed in C. albicans biofilms grown on serum-free controls, 3) Antifungal susceptibility tests demonstrated that (×3MIC) amphotericin B, (×24MIC) Itraconazole and (×12MIC) ketoconazole and fluconazole killed approximately 50% of 48h C. albicans biofilms on serum coated CVCs. Furthermore amphotericin B in association with ketoconazole exhibited effective synergistic killing of biofilm Candida compared with the combined effect of amphotericin B with either itraconazole or fluconazole.

Conclusion: Serum noticeably enhances the upregulation of genes crucial for biofilm development.