Determination of antibacterial effect of metal and carbon-based nanomaterials in in vitro conditions

Ventilation tubes implanted in the eardrum in the treatment of otitis media are used to ventilate the ear cavity and remove accumulated fluids. However, bacterial adhesion and biofilm formation had been obsereved on ventilation tube surfaces by autopathogenic bacteria over time. In this study, antibacterial activities of metal and carbon-based nanomaterial coatings on ventilation tube surfaces, which are thought to prevent formation of bacterial biofilm, have been investigated in vitro. Antibacterial activities of 0.1%, 0.3% and 0.5% concentrations of nickel oxide, zinc oxide, silicon dioxide and graphene oxide (GO), reduced graphene oxide (rGO), GO nanoribbon, rGO nanoribbon nanomaterials coated on silicon discs were measured against Pseudomonas aeruginosa ATCC 19142 and Staphylococcus aureus ATCC 25923 test bacteria using agar disc diffusion method. It has been observed that metal-based nanomaterials coated on silicon discs reduce growth in both test bacteria, whereas carbon-based nanomaterials do not have any antibacterial effect. In our study, antibacterial activities of suspensions containing 0.5%, 1% and 1.5% concentrations of metal and carbon based nanomaterials were also investigated using agar disc diffusion and agar well diffusion methods. While high antibacterial activity was observed in the agar well diffusion method in both test bacteria of metal-based nanomaterials and it was observed that the carbon-based nanomaterials had no antibacterial activity in both methods and on both test bacteria. Optimization of the quantitative measurement of in vitro biofilm formation in fluoroplastic ventilation tubes was done with an initial inoculum containing 10⁷ cfu/ml for P. aeruginosa and 10⁸ cfu/ml for S. aureus and at 4-days incubation period. In addition, centrifugation followed by ultrasonication and repeated vortex has been identified as the best method for removing biofilm from ventilation tube surfaces.