Determination of the mechanism of photoinduced toxicity of selected metal oxide nanoparticles (ZnO, CuO, Co3O4 and TiO2) to E. coli bacteria

Cytotoxicity of selected metal oxide nanoparticles (MNPs) (ZnO, CuO, Co₃O₄ and TiO₂) was investigated in Escherichia coli both under light and dark conditions. Cytotoxicity experiments were conducted with spread plate counting and the LC₅₀ values were calculated. We determined the mechanism of toxicity via measurements of oxidative stress, reduced glutathione, lipid peroxidation, and metal ions. The overall ranking of the LC₅₀ values was in the order of ZnO3O₄2 under dark condition and ZnO23O₄ under light condition. ZnO MNPs were the most toxic among the tested nanoparticles. Our results indicate depletion of reduced glutathione level and elevation of malondialdehyde level correlated with the increase in oxidative stress. Released metal ions were found to have partial effect on the toxicity of MNPs to E. coli. In summary, the dynamic interactions of multiple mechanisms lead to the toxicity of the tested MNPs to E. coli.