Effects of metal oxide nanoparticles with plant extract on viability of foodborne pathogens

The present study tested the antibacterial activity, expressed as minimum bactericidal concentration (MBC), of zinc oxide nanoparticles (ZnO-NPs), copper oxide nanoparticles (CuO-NPs) and their combination with or without rosemary, clove or cinnamon extract against Escherichia coli O157:H7 and Listeria monocytogenes. The NPs were characterized by scanning electron microscopy. The sizes of ZnO-NPs and CuO-NPs were in the range of 56–71 and 171–204 nm, respectively. Results showed that ZnO-NPs had a greater inhibitory effect against both E. coli O157:H7 and L. monocytogenes than CuO-NPs. The MBC of ZnO-NPs against E. coli O157:H7 and L. monocytogenes was 300 and 350 μg/mL, respectively, while the MBC of CuO-NPs was >1,000 and 400 μg/mL, respectively. When combined, ZnO-NPs and CuO-NPs had additional inhibitory effects against L. monocytogenes, but not against E. coli O157:H7. In general, the antibacterial activity of the NPs against E. coli O157:H7 and L. monocytogenes was enhanced by rosemary or cinnamon extract. Incorporation of clove extract into the NPs improved the antibacterial effect against E. coli O157:H7, but not against L. monocytogenes. Thus, plant extracts may be useful adjuncts for the synthesis of ZnO-NPs or CuO-NPs which can be used to control foodborne pathogens. Practical Application: Incorporation of plant extracts in the synthesis of metal oxide nanoparticles (NPs) can be applied to improve the antimicrobial activity of NPs against foodborne pathogens.