Mechanism of enhanced antibacterial activity of ultra-fine ZnO in phosphate buffer solution with various organic acids☆

Abstract Ultra-fine-ZnO showed low toxicity in complex water matrix containing multiple components such as PBS buffer and the toxic mechanism of ultra-fine-ZnO has not been clearly elucidated. In present study, enhanced antibacterial activity of 200 nm diameter ultra-fine-ZnO in PBS buffer against Bacillus cereus and Escherichia coli were observed in the presence of several organic acids in comparison with ultra-fine-ZnO in PBS buffer alone. These findings indicated that the toxic effects of the ultra-fine-ZnO was dependent on the concentration of released Zn 2+ which was affected by organic acids. The production of reactive oxygen species (ROS) did not responsible to the toxic mechanism of ultra-fine-ZnO which was tested using the antioxidant N -Acetylcysteine (NAC). Indeed, ultra-fine-ZnO induced bacteria cell membrane leakages and cell morphology damages that eventually led to cell death, which were confirmed using propidium monoazide (PMA) in combination with PCR and scanning electron microscopy (SEM). All data gathered herein suggested that released Zn 2+ played a major role in the microbial toxicity of ultra-fine-ZnO.