Applied Microbiology

Biofilms often lead to significant problems in clinical settings as they are hard to remove from surfaces (e.g., catheters) and the show increased antimicrobial resistances. Staphylococcus aureus (strain DSM-799 and Newman) biofilms were grown for 48 hours in different concentrations of CuCl2 or CuSO4 in order to establish a copper value giving a breakpoint for cell growth. Electrical

impedance sensing (EIS) was performed using an ECIS Model Z Theta (Ibidi, Germany). Biofilms were grown in eight well arrays with ten electrodes per well. Starting value impedance was measured using 150 μL of LB media and 150 μL of the copper solution in the desired concentration. This step was done for all eight cells and the solution was carefully removed with a pipette after the measurement. Afterwards, again 150 μL of the desired copper concentration were added to the empty cells and inoculated with 150

μL of the diluted ONC (OD600 of 0.5). Impedance was measured directly afterwards and after 24 and 48 hours of incubation at 37 °C and 90 rpm. Additionally typical laboratory measurements for biofilms (polysaccharide and protein content, life/dead cell flowcytometry) were performed. When uninfluenced, biofilms develop on the electrodes of the system, blocking the electrodes, causing the impedance values to drop. When cell growth and biofilm formation becomes inhibited this drop does not take place. These

findings are supported by the data of the other measurement techniques. Future studies will evaluate the feasibility of the presented method for use in routine antimicrobial assessment. Other species and different antimicrobial substances will be used.