Differentiating the mechanism of antibacterial activities of nano and ionic copper by using Escherichia coli as a model microorganism

In this study, the effect of polymer stabilized copper nanoparticles and ionic copper on the growth, nucleic acid pool, reactive oxygen species generation, cell surface lipopolysaccharide, outer membrane protein profile and cell surface morphology of Escherichia coli were investigated. Copper nanoparticles exhibited a superior bactericidal activity associated with increased nucleic acid degradation, reactive oxygen species generation and change in the outer membrane protein profile compared to ionic copper in a concentration dependent manner. Although, there was no change in the outer membrane lipopolysaccharide profile, inductively coupled plasma mass spectrometry analysis of nano- and ionic copper treated Escherichia coli cells revealed that more amounts of copper nanoparticles were transported inside the cells compared to the ionic counterpart up to 500 M concentrations. Interestingly, copper nanoparticles at 1000 M concentration could induce membrane pit formation whereas ionic copper failed to exhibit such property under the same experimental conditions. Based on these observations it can be concluded that both nano- and ionic copper exert their antibacterial action through the generation of reactive oxygen species, degradation of cellular nucleic acids and alteration of membrane protein profile, but with a significant difference in the effective concentration range due to the differential cellular transport.