Antimicrobial Efficacy of Zinc Oxide Quantum Dots against Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7

Abstract

ABSTRACT: Zinc oxide quantum dots (ZnO QDs) are nanoparticles of purified powdered ZnO. These were evaluated for antimicrobial activity against Listeria monocytogenes , Salmonella Enteritidis, and Escherichia coli O157:H7. The ZnO QDs were utilized as a powder, bound in a polystyrene film (ZnO‐PS), or suspended in a polyvinylprolidone gel (ZnO‐PVP). Bacteria cultures were inoculated into culture media or liquid egg white (LEW) and incubated at 22 °C. The inhibitory efficacies of ZnO QDs against 3 pathogens were concentration dependent and also related to type of application. The ZnO‐PVP (3.2 mg ZnO/mL) treatment resulted in 5.3 log reduction of L. monocytogenes and 6.0 log reduction of E. coli O157:H7 in growth media after 48 h incubation, as compared to the controls. Listeria cells in the LEW control increased from 3.8 to 7.2 log CFU/mL during 8 d incubation, while the cells in the samples treated with 1.12 and 0.28 mg ZnO/mL were reduced to 1.4 and 3.0 log CFU/mL, respectively. After 8 d incubation, the cell populations of Salmonella in LEW in the presence of 1.12 and 0.28 mg ZnO/mL were reduced by 6.1 and 4.1 log CFU/mL over that of controls, respectively. ZnO powder and ZnO‐PVP showed significant antimicrobial activities against all 3 pathogens in growth media and LEW. ZnO‐PVP coating had less inhibitory effect than the direct addition of ZnO‐PVP. No antimicrobial activities of ZnO‐PS film were observed. This study suggested that the application of ZnO nanoparticles in food systems may be effective at inhibiting certain pathogens.