Investigating antimicrobial stress responses in Escherichia coli induced by high-frequency ultrasound

Soyler, I., Costello-Gould, K., Karatzas, K.-A. G., Gutierrez-Merino, J. and Bussemaker, M. (2026) Investigating antimicrobial stress responses in Escherichia coli induced by high-frequency ultrasound. Ultrasonics Sonochemistry, 132. 107935. ISSN 1873-2828 doi: 10.1016/j.ultsonch.2026.107935

Abstract/Summary

The antimicrobial mechanisms of high-frequency ultrasound (HFUS) under low-power conditions were investigated using Escherichia coli as a model foodborne pathogen, with oxidative and physical contributions evaluated through radical scavenger assays, intracellular reactive oxygen species (ROS) quantification, flow cytometry, and scanning electron microscopy. Bacterial inactivation was strongly frequency-dependent. 760 kHz induced greater intracellular ROS accumulation and membrane permeabilisation than 500 kHz, and radical scavenger experiments confirmed a major ROS contribution to inactivation. The combination of HFUS (760 kHz, 30 W) with epigallocatechin gallate (EGCG; 0.2 mg/mL) produced synergistic antibacterial efficacy, accompanied by enhanced membrane depolarisation, permeabilisation, and ultrastructural damage. Pre-exposure to ultrasound increased bacterial sensitivity to subsequent lethal thermal (56◦C) and oxidative (10 mM H2O2) challenges. Mutant analysis of eight E. coli K-12 strains revealed that antioxidant defence systems, particularly glutathione reductase (gor), were critical for survival, while deletion of the general stress regulator rpoS or oxidoreductase grxA increased tolerance, indicating complex interacting stress-response mechanisms. Overall, HFUS inactivation is driven primarily by a combination of chemical and physical mechanisms, encompassing ROS-mediated oxidative damage and cavitation-induced membrane disruption, enhancing bacterial susceptibility to additional antimicrobial stresses, and therefore holds greater potential as a complementary technology than as a stand-alone treatment.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/131156
Identification Number/DOI	10.1016/j.ultsonch.2026.107935
Refereed	Yes
Divisions	Life Sciences > School of Chemistry, Food and Pharmacy > Department of Food and Nutritional Sciences > Food Microbial Sciences Research Group
Publisher	Elsevier
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