Effect of Ultrasound Combined with Plasma-Activated Water on Lethal and Sublethal Injury Against Escherichia coli

Plasma-activated water (PAW) treatment is a promising technique for food processing, but it causes sublethal injury (SI) to microorganisms. This study investigated the effect of ultrasound (US) combined with PAW (US-PAW) on SI of Escherichia coli (E. coli). Results showed that, after plasma activation for 10 min and treatment for 10 min, the US-PAW treatment caused a 4.89 ± 0.07 log CFU/mL reduction in E. coli. Meanwhile, under these conditions, the SI rate of E. coli was decreased to 13.3 ± 2.15%, significantly reduced by 52.74% compared to using PAW alone. The inactivation process of US-PAW treatment fitted the Weibull model better. The morphology of E. coli was destroyed by PAW and US-PAW treatment. Additionally, US-PAW treatment significantly increased the leakage of protein and nucleic acid, as well as cell membrane permeability and potential. Compared to PAW or US treatment, the proportion of membrane fatty acids and the structure of membrane proteins were altered in the US-PAW group. Furthermore, intracellular reactive oxygen species (ROS) levels increased by US-PAW treatment, and the levels of GSH, SOD, and CAT enzyme activities were significantly reduced, compared to PAW or US treatment. The combined treatment also resulted in significant DNA oxidative damage. The disruption of cell membrane structure and oxidative damage caused by US-PAW treatment resulted in irreversible damage to bacteria, thus reducing the SI rate.