The resistance of bacteria towards traditional antibiotics currently constitutes one of the most important health care issues with serious negative impacts in practice. Overcoming this issue can be achieved by using antibacterial agents with multimode antibacterial action. Silver nano-particles (AgNPs) are one of the well-known antibacterial substances showing such multimode antibacterial action. Therefore, AgNPs are suitable candidates for use in combinations with traditional antibiotics in order to improve their antibacterial action. In this work, a systematic study quantifying the synergistic effects of antibiotics with different modes of action and different chemical structures in combination with AgNPs against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus was performed. Employing the microdilution method as more suitable and reliable than the disc diffusion method, strong synergistic effects were shown for all tested antibiotics combined with AgNPs at very low concentrations of both antibiotics and AgNPs. No trends were observed for synergistic effects of antibiotics with different modes of action and different chemical structures in combination with AgNPs, indicating non-specific synergistic effects. Moreover, a very low amount of silver is needed for effective antibacterial action of the antibiotics, which represents an important finding for potential medical applications due to the negligible cytotoxic effect of AgNPs towards human cells at these concentration levels.

Department of Environmental Microbiology Institute for Ecology of Industrial Areas Kossutha 6 40 844 Katowice Poland

Department of Microbiology Faculty of Medicine and Dentistry Palacký University in Olomouc Hněvotínská 5 775 15 Olomouc Czech Republic

Regional Centre of Advanced Technologies and Materials Department of Experimental Physics and Physical Chemistry faculty of Science Palacký University in Olomouc 17 listopadu 12 771 46 Olomouc Czech Republic

Regional Centre of Advanced Technologies and Materials Department of Physical Chemistry Faculty of Science Palacký University in Olomouc 17 listopadu 12 771 46 Olomouc Czech Republic

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