Purpose: The increase of bacterial resistance to common antibacterial agents is one of the major problems of health care systems and hospital infection control programs. In this study, antimicrobial activity of titanium dioxide (TiO₂ ) and zinc oxide (ZnO) nanoparticles (NPs) was investigated against E. coli, Salmonella enteritidis, Listeria monocytogenes, and Staphylococcus aureus pathogenic bacteria by determining sensitivity coefficient and kinetics of bacterial death. Methods: Antimicrobial tests were performed with ~10⁶ CFU/mL of each bacterium at baseline. At first, minimum inhibitory concentration (MIC) was concluded by the dilution method and then, death kinetic and susceptibility coefficient of NPs suspensions was determined at 0 to 360 min. treatment time. Results: The results of this study revealed that, the highest susceptibility was observed for L. monocytogenes (Z=0.025 mL/μg) to TiO₂ NPs, whereas the lowest susceptibility was obtained in the reaction of ZnO NPs with S. enteritidis (Z=0.0033 mL/μg). The process of bacterial death in NPs suspension was assumed to follow first-degree kinetic and the survival ratio of bacteria decreased by the increase in treatment time. An increase in the concentration of NPs was seen to enhance the bactericidal action. Conclusion: Results showed that L. monocytogenes had higher sensitivity compared to S. enteritidis. The results of this study also demonstrated that TiO₂ NPs have a strong antimicrobial effect in comparison with ZnO NPs and it could be employed to aid the control of pathogenic bacteria.

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