Objective: To study the effect of ultra high pressure (UHP) on the cell membrane of Listeria monocytogenes.
Methods: We treated L. monocytogenes with different hydra high pressure from 100 to 500 MPa at 25 degrees C for 15 min. Then we determined the rate of cell inactivation by viable cell counts. We compared the morphological changes of treated and untreated cells using transmission electron microscopy (TEM). We evaluated the membrane permeability by release of potassium ion (K+) or magnesium ion (Mg2+), UV-absorbing substances and uptake of the fluorescent dye propidium iodide (PI). We measured these parameters by spectrofluorometry, UV-spectrophotometer and atomic absorption spectrophotometer (AAS). We used Na+/K(+)-ATPase kit to measure the activity of Na+/K(+)-ATPase.
Results: The pressure treatment at 300, 350 and 400 MPa reduced the population of the bacteria from 9.00 to 5.20, 3.27 and 1.35 Log CFU respectively, and no viable cells could be detected at 450 MPa. The structure changes revealed by TEM show that the cell membrane was damaged, the cell wall was breached and the cytoplasm aggregated and a large electron transmission area appeared which bring about the release of UV-absorbing substances, K+ and Mg2+ ions. Besides, the activity of Na+/K(+)-ATPase was also decreased by UHP.
Conclusion: UHP could kill L. monocytogenes.