In Vitro ingrowth of yeasts into medical grade silicone rubber

Shunt-valves made of silicone rubber are placed between the trachea and the oesophagus in order to allow patients after laryngectomy to produce voice again. The oesophageal side of the shunt-valve, however, becomes rapidly colonized by a biofilm, consisting of bacteria and yeasts. Electron microscopy on explanted shunt-valves demonstrates that the yeast show ingrowth into the silicone rubber. Surface treatment of the silicone rubber is often suggested to be a pathway to reduce adhesion and ingrowth of yeasts to prostheses. An effective development of such a treatment requires an in vitro system by which similar defects as found in vivo can be created under laboratory conditions. Candida tropicalis, isolated from an explanted prosthesis, could be made to grow into the silicone rubber under laboratory conditions by the removal of all nutrients using a modified Robbins device. After the removal of all nutrients, the yeast cells adapted a filamentous growth form. Only filamentously growing yeasts appeared to be able to penetrate the silicone rubber.