In vitro evaluation of silver-coated silicone tracheobronchial stents on growth and attachment of clinical isolates

OBJECTIVES Silicone stents are used for treating obstructions of the central airways. Bacterial colonization can result in halitosis, respiratory infections and sepsis. The main objectives were to determine the microorganisms involved in stent colonization and to evaluate silver-coating as a mechanism to reduce bacterial growth and adhesion. METHODOLOGY Clinical isolates were obtained from bronchial washing (BW) in 32 patients after 1 month of stenting. Silver was deposited on PDMS (polydimethylsiloxane) using plasma treatment. Silicone and silver-coated silicone slides were covered with 10 6 cfu/ml bacterial cultures and incubated 24h at 37°C. Viability of adhered bacteria was assessed by confocal examination of Live/Dead staining on Pseudomonas aeruginosa (PA01 strain & clinical isolates) and Staphylococcus aureus clinical isolates. RESULTS The main microorganisms isolated from BW were P. aeruginosa (22%), S. viridans (22%) and S. aureus (15%) . After 24h of static growth, bacteria adhered to silver-coated slides were dead in contrast to bacteria on uncoated silicone slides. Clinical isolates were more resistant to silver than the P. aeruginosa PA01 strain used for these experiments, with the need of concentrations 0.8-0.9 µg/mm 2 for the clinical P. aeruginosa isolates, >1 µg/mm 2 for S. aureus and 0.4 µg/mm 2 for PA01. CONCLUSIONS S. aureus and P. aeruginosa were the main pathogens associated to tracheobronchial silicone stent colonization. Clinical pathogens were more resistant to silver-mediated killing than PA01, with a silver concentration above 1 µg/mm 2 needed to kill clinical pathogens adhered to the silver-coated silicone slides.