Abstract: The mechanism of action of ultrasound (US) combined with slightly acidic electrolyzed water (SAEW) treatment against Shewanella putrefaciens was studied. The spoilage causing bacterium Shewanella putrefaciens was treated with US, SAEW or US + SAEW for 10 min, and untreated cells suspended in sterile normal saline was used as a control. The changes in the cell membrane and internal environment of this bacterium were evaluated by measuring the reduction in bacterial count, bacterial growth curve, electrical conductivity, propidium iodide (PI) intake, alkaline phosphatase (AKP) and lactate dehydrogenase (LDH) activity, the leakage of ultraviolet-absorbing materials. The microstructure was also observed by scanning electron microscopy (SEM) before and after treatment. The results showed that US + SAEW treatment reduced the bacterial count by 2.48 (lg (CFU/mL)). Compared with the control and single treatment groups, US + SAEW greatly damaged the cell membrane integrity, causing the leakage of intracellular components and a significant increase in electrical conductivity, AKP and LDH activity (P < 0.05). After US + SAEW treatment, the bacterial cells collapsed obviously, the outer membrane was broken, the cell wall was damaged, and a large amount of cellular contents leaked out of the cells. Therefore, ultrasonic treatment can seriously damage the cell wall and cell membrane of Shewanella putrefaciens, promoting SAEW to enter into cells, enhancing the bactericidal efficacy, and leading to cell death eventually.

Key words: ultrasound; slightly acidic electrolyzed water; Shewanella putrefaciens; action mechanism