Induction of Candida albicans biofilm formation on silver-coated vascular grafts

Silver exhibits excellent antimicrobial properties and is used to protect medical devices from microbial colonization. Because few data are available on the influence of silver coating of vascular prostheses on Candida biofilm formation, this study aimed to investigate the effect of silver on yeast biofilm formation in an in vitro model. Prosthesis material was co-cultivated with two different strains of Candida albicans and the effect of silver on attachment and the growth of biofilms was monitored by microscopy and by quantification of cfu and mitochondrial dehydrogenase activity. Silver collagen-coated vascular prostheses significantly reduced C. albicans biofilm formation in serum-free medium. Paradoxically, in the presence of 50 serum, silver increased the growth of biofilms on silver-containing prostheses 2- to 10-fold compared with silver-free prostheses. Silver ion concentrations between 1.7 and 0.17 mg/L, corresponding roughly to 1/20 to 1/200 of the MIC of silver nitrate, stimulated biofilm formation by C. albicans. Serum proteins reduced the concentration of silver ions delivered from the surface of vascular prostheses to a subinhibitory level, which stimulated the attachment and biofilm formation of C. albicans on grafts. Silver collagen coating therefore seems to be unsuitable for the prevention of growth of C. albicans on vascular prostheses under physiological conditions.