An investigation into the electro‐tolerance of Escherichia coli treated by radio frequency electric fields

Abstract

BACKGROUND Radio frequency electric field (RFEF) is a novel technology for the microbial disinfection of liquids such as water and fruit juices. Here we investigated the development of microbial tolerance against RFEF to assess the long‐term suitability of this technology. We applied a constant electric field, outlet temperature and treatment time of 14 kV cm−1, 40 °C and 1.275 ms, respectively, to Escherichia coli inoculated in saline water to observe whether the descendants of the surviving bacteria could develop tolerance against RFEF. Escherichia coli that survived the RFEF treatment were recultivated and treated under similar processing conditions for 15 generations. RESULTS The results showed that although inactivation levels due to RFEF treatments fluctuated during consecutive generations, no significant difference between inactivation at cycles 1 and 15 was observed. Furthermore, inactivation levels during consecutive generations hovered around an average value of 2.18 log10 CFU mL−1. For short‐term effect, which compared untreated cells to treated ones at cycle 1, proteomics showed mixed trends of up‐ and down‐regulated differentially expressed proteins (DEPs). However, in the long term, which compared treated cells at cycles 1 and 15, DEPs involved in stress response, cell wall structure and antioxidant activities were all up‐regulated. CONCLUSION The results indicate that although cell wall is the main target for the effect of electric field, they suggest that, in the long term, oxidative stress may also be induced. © 2022 Society of Chemical Industry (SCI).