Introduction:
Due to the aging of the population, the number of patients with chronic diseases like diabetes mellitus 2 type, atherosclerosis, venous insufficiency is becoming more severe. All these factors of poor blood supply, as well as a bedridden regimen in inpatient treatment facilities, lead to more chronic infected non-healing ulcers and pressure sores. Chronic infectious ulcers (CIU) lead to high health costs, as well as patient suffering. An especially big problem is the resistance of bacteria to antibiotics. As an alternative to traditional antibiotics, nanoparticles of various metals can be used. Recent studies have shown that there is a synergistic antibacterial effect between silver and some transition metals, such as copper, but synergic effect between metal nanoparticles with different functional groups is not described yet.

Material and Methods:
In this project we studied antibacterial effect of silver and copper nanoparticles with different functional groups applying determination of minimal bactericidal concentration. Bacteria Escherichia coli K-12 and pathogenic Pseudomonas aeruginosa PAO1, Staphylococcus aureus ATCC 25923 and multiresistant ESBL Escherichia coli were used as models. Toxicity of the same nanoparticles and their combinations was also compared using Resazurin test with murine fibroblasts Balb/c T3T.

Results:
We showed that silver and copper nanoparticles were synergistic in killing all tested bacteria. The antibacterial effect of the mixture of nanoparticles was up to 5 times higher than the sum of antibacterial effects of components separately. Especially high synergy with silver was observed in combination with copper nanoparticles with positively charged functional coating. The difference in synergy between negatively and positively charged nanoparticles was especially relevant for Gram-positive bacteria. Unfortunately, the synergy was not specific for bacterial cells, but also killed mammalian cells in vitro. That can be a problem in developing safe antibacterials for practical use. Hopefully, future investigations of synergy mechanisms can help to develop new safe and effective antibacterial nanocomposites.