Sensitivity Coefficient and Death Kinetics of Escherichia Coli and Staphylococcus Aureus to Zinc Oxide and Copper Oxide Nanoparticles

Increasing bacterial resistance to usual antibacterial agents is a major problem of health care systems. Controlling the spread of bacteria within a hospital is thus a constant challenge. In this study, we investigated antimicrobial activity of copper oxide (CuO) and zinc oxide (ZnO) nanoparticles against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 bacteria. In this study, sensitivity coefficients and death kinetics of nanoparticles were used to evaluate the antimicrobial characteristics of ZnO and CuO nanoparticles against Escherichia coli and Staphylococcus aureus. Antimicrobial tests were performed with 108 CFU/ml of each bacterium at baseline. At first, minimum inhibitory concentration (MIC) was determined. Then, nanoparticle suspension of one and two times of MIC was used to determine death kinetics and sensitivity coefficient at treatment time of 0 to 360 minutes. In reaction with Staphylococcus aureus, ZnO nanoparticles (size: 20 nm) had the highest susceptibility (Z = 0.033 ml/μg) while CuO nanoparticles (size: 60 nm) had the lowest susceptibility (Z = 0.0032 ml/μg). The process of Escherichia coli and Staphylococcus aureus death in CuO and ZnO suspension was assumed to follow first-order kinetic. The survival ratio of bacteria decreased with increasing treatment time. An increase in the concentration of nanoparticles enhanced bactericidal properties. The sensitivity of Staphylococcus aureus to ZnO and CuO nanoparticles was higher than Escherichia coli. The results of this study demonstrated that ZnO has a strong antimicrobial effect compared to CuO.