Abstract: This study aimed to investigate the synergistic bactericidal effect and mechanism of ultrasound combined with ultraviolet against Escherichia coli O157:H7. The inactivation kinetics was modeled, ultrastructural changes in bacterial cells were examined as well as alterations in the properties of the cell membrane, and oxidative stress levels were determined. The results revealed that after 40 s of combined treatment, the bacterial count was reduced by 8.3 (lg (CFU/mL)). Significant impairment of cell morphology and leakage of cellular contents were observed. The combined treatment induced a cellular stress response within a short period of time, characterized by increased cellular esterase activity, ATP content and levels of reactive oxygen species (ROS) along with DNA damage. In conclusion, combined treatment with ultrasound and ultraviolet synergistically exerted a significant bactericidal effect. Ultrasound-induced cavitation enhances structural damage to cells, enabling ultraviolet to directly act on DNA. Moreover, both treatments work together to exacerbate oxidative stress, thereby interfering with cellular metabolism and exerting a synergistic bactericidal effect.

Key words: ultrasound; ultraviolet; Escherichia coli O157:H7; bactericidal mechanism; synergistic effect