Copper nanoparticles toxicity: Laboratory strains verses environmental bacterial isolates.

Nanoparticles have emerged as significant environmental contaminants and their impact has been studied using laboratory strains of bacteria. This study focuses on investigating the response of environmental isolate and laboratory strains of E. coli to 50 and 100 nm size of copper nanoparticles (CuNPs). The laboratory cultures included pathogenic and non-pathogenic strains. The environmental isolate and the non-pathogenic E. coli strain showed different inactivation patterns. After 2 h exposure to 50 nm CuNPs, the environmental isolate and the lab strain of E. coli lost 7.22 and 6.47 log; whereas the reduction of 6.16 and 6.68 log resulted after exposure to 100 nm CuNPs, respectively. The pathogenic E. coli O157:H7 exposed to 50 and 100 nm CuNPs for 2 h resulted in 5.24 and 6.54 log reduction, respectively. Although the environmental isolate and the laboratory strains of E. coli showed similar inactivation trends; they exhibited different toxicity elicitation mechanisms after exposure to the CuNPs. The pathogenic and non-pathogenic strains elicited significantly different levels of glutathione reductase (GR) activities, an enzyme critical for protection against radicals. Similarly, the environmental isolate and the lab strains of E. coli exhibited opposite trend in GR activities. These results clearly indicate divergence in the toxicity elicitation in the environmental isolate versus the laboratory strains from exposure to CuNPs, which highlights the need for an in-depth investigation of the impact of NPs on the biological processes and long-term effect of high load of NPs on the stability of aquatic and terrestrial ecologies.