Study of antimicrobial activity and mechanism of zinc oxide nanoparticles against foodborne pathogens

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Antimicrobial activities of zinc oxide nanoparticles (ZnO NPs) and their mode of action against an important foodborne bacterium (E. coli O157:H7) and two postharvest pathogenic fungi (Botrytis cinerea and were investigated in this study. ZnO NPs with sizes of 70 [plus or minus] 15 nm and concentrations from 0 to 12 mmol l[superscript -1] were used in this study. A battery of methods including traditional microbiological plating, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy were used to study of ZnO NPs and to characterize the changes in morphology and cellular compositions of bacterial and fungal cells treated with ZnO NPs. Results show that ZnO NPs at concentrations greater than 3 mmol l[superscript -1] can significantly inhibit the growth of both bacteria and fungi. The inhibitory effects of ZnO NPs against E. coli O157:H7 increased as the concentration of ZnO NPs increased. Results indicate that ZnO NPs may distort and damage bacterial cell membrane, resulting in a leakage of intracellular contents and eventually the death of bacterial cells. P. expansum was more sensitive to the treatment with ZnO NPs than B. cinerea. SEM images and Raman spectra obtained in this study indicate two different antifungal mechanisms of ZnO NPs against B. cinerea and P. expansum. ZnO NPs inhibited the growth of B. cinerea by releasing nucleic acids, which caused tumor-like structures in fungal cells. In comparison, ZnO NPs prevented the development of conidiophores and conidium of P. expansum, which eventually led to the death of fungal cells. These results suggest that ZnO NPs could potentially be used as an effective antimicrobial agent in agricultural and food safety applications.