Bacterial biofilm formation on cochlear implants in vitro

The formation of bacterial biofilms on medical devices, such as cochlear implants, can lead to chronic and therapy-refractory infections. In this study, various surfaces of three commercially available CIs from different manufacturers were examined for bacterial biofilm formation and reduction of a preexisting biofilm by application of bioactive glass.

Four bacterial species were tested: Pseudomonas aeruginosa (ATCC9027), Staphylococcus aureus (ATCC6538), Staphylococcus epidermidis (ATCC12228) and Streptococcus pyogenes (ATCC19615). Biofilms were formed over 24h in tryptic soy broth at 36 °C. Therefore, 2 ml of a cell suspension with an inoculum between 5 × 105 and 5 × 106 cells were added to implant surfaces, using a 6-well, flat-bottomed polystyrene microtiter plate. Biofilm formation was detected by staining with crystal violet followed by destaining with acetic acid and measurement of the solution's optical density at 620nm. For Pseudomonas aeruginosa and Staphylococcus aureus biofilm reduction after application of bioactive glass was detected.

The highest biofilm formation rate was attained from P. aeruginosa and S. pyogenes on platinum foil, as well as on several silicone components. S. epidermidis and S. aureus showed a lower biofilm formation rate compared to both other species. For Pseudomonas aeruginosa and Staphylococcus aureus a significant reduction in biofilm formation was detected under application of bioactive glass.

The tested bacteria displayed biofilm formation on the CI surfaces in a species- and material-specific manner. Our results show that bioactive glass is capable of reducing biofilm formation on CI materials in vitro. It is a challenging and promising task to test the clinical relevance of these experiments in the future.

Publication History

Publication Date:
18 April 2018 (online)