Effect of plasma-activated solution treatment on cell biology of Staphylococcus aureus and quality of fresh lettuces

Authors: ZHAO, JIANYING - Nanjing Agricultural University; QIAN, JING - Nanjing Agricultural University; Zhuang, Hong; LUO, JI - Nanjing Agricultural University; HUANG, MINGMING - Nanjing Agricultural University; YAN, WENJING - Nanjing Agricultural University; ZHANG, JIANHAO - Nanjing Agricultural University

Submitted to: Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2021
Publication Date: 12/3/2021
Citation: Zhao, J., Qian, J., Zhuang, H., Luo, J., Huang, M., Yan, W., Zhang, J. 2021. Effect of plasma-activated solution treatment on cell biology of Staphylococcus aureus and quality of fresh lettuces. Foods. 10(12):2976. https://doi.org/10.3390/foods1012297610.3390/foods10122976.
DOI: https://doi.org/10.3390/foods1012297610.3390/foods10122976

Interpretive Summary: Plasma-activated solution (PAS) is a liquid treated with plasma. PAS has low pH and high oxidation-reduction potential, and is rich in reactive oxygen and nitrogen species (H2O2, O3, NOx). These characteristics have been proved to be effective against spoilage bacteria and pathogens. The consumption of ready-to-eat vegetables with minimal processing such as lettuces has significantly increased due to the abundant amount of vitamins and minerals. However, contaminated minimally processed vegetables are responsible for the numerous outbreaks of food poisoning and food-related infections. Therefore, there is strong interest in developing a sanitizer to reduce microbial contamination and maintain quality of minimally processed vegetables. The objective of the present study was to investigate the effects of PAS on the Gram-positive pathogen Staphylococcus aureus and quality of fresh lettuce leaves. Our data show that PAS could effectively inactivate the pathogen S. aureus, damage bacterial cells, and result in oxidation of bacterial cell wall, cell membrane, and cellular DNA. PAS treatment does not only improve microbiological quality of fresh lettuce leaves, but also has no negative effects on the nutrient contents and appearance of treated leaves. PAS can be used as an alternative sanitizer for non-thermally disinfecting microbiota and food-borne pathogens and improving the quality of fresh fruits and vegetables.

Technical Abstract: This study aimed to investigate effects of plasma-activated solution (PAS) on cell biology of a Gram-positive (G+) bacterium Staphylococcus aureus and quality of fresh lettuce leaves. PAS was prepared by dielectric barrier discharge (DBD) plasma and either incubated with S. aureus for 10-30 min or with lettuce leaves for 10 min. The effects on the cell biology were evaluated with electron microscopic images, cell leakage, chemical modification of cellular components. The effects on lettuce quality were estimated with microbial population, color, vitamin C, and leaf surface integrity. PAS reduced S. aureus population by as great as 4.95-log cycles and resulted in irregular and incomplete outlines of bacterial cells and increased cell leakage. It also resulted in increased contents of reactive oxygen species (ROSs) in cells, the C-O bonds in cell wall, and 8-hydroxydeoxyguanosine content in cellular DNA and reduced ratios of unsaturated/saturated fatty acids in cell membrane. PAS treatment reduced bacterial load on fresh lettuce and had no negative effects on the quality. Data from this study suggest that the oxidation of cellular components by PAS may be responsible for death of treated G+ bacteria and PAS can be used for disinfection of ready-to-eat fresh vegetables.