In vitro formation of oropharyngeal biofilms on silicone rubber treated with a palladium/tin salt mixture

Abstract

Adhesion of yeasts and bacteria to silicone rubber is one of the first steps in the biodeterioration of indwelling, silicone rubber voice prostheses. In this paper, silicone rubber, so-called "Groningen button," voice prostheses were treated with a colloidal palladium/tin solution to form a thin metal coat intended to discourage biofilm formation. First it was demonstrated that this treatment did not negatively affect the airflow resistance of the prostheses or induce any cytotoxicity. Subsequently, palladium/tin-treated voice prostheses were placed in a modified Robbins device together with untreated control prostheses to evaluate biofilm formation. Biofilms were formed by inoculating the device for 3 days with the total cultivable microflora obtained from an explanted, malfunctioning voice prosthesis supplemented with separately isolated yeasts (Candida albicans and Candida tropicalis). After 3 days the device was perfused three times daily with growth medium and phosphate-buffered saline. The device was allowed to drain between perfusions to better mimic the conditions in the oropharynx (moist but not always fully wetted). After 9 days the total number of bacterial and fungal colony-forming units on the prostheses were determined microbiologically, and scanning electron micrographs were taken of the valve sides. Biofilm formation was significantly less on the heavily treated palladium/tin prostheses than it was on the untreated prostheses although some ingrowing microcolonies also were observed on the treated prostheses. The spread of the biofilms was smaller on the treated prostheses than on the untreated ones.