Abstract: This study investigated the membrane injury of Escherichia coli O157:H7 cells exposed to high hydrostatic pressure. Different pressure levels (200, 400 and 500 MPa) were used to evaluate the inactivation of the bacteria. The leakage of nucleic acids, K+ and Mg2+, and propidium iodide (PI) intake of the cells, as well as changes in Na+/K+-ATPase and Ca2+/Mg2+-ATPase activities were determined after pressure treatment. Results indicated that, after 200 and 400 MPa treatments for 5 min, the number of viable cells decreased from an initial level of 8.8 to 8.2 and 6.3 (lg(CFU/mL)), respectively. When treated at 500 MPa, no viable cells were detected on plate count agar. As the pressure level rose, the leakage of intratracellular constituents and the fluorescence (OD) of PI intake increased significantly and both enzyme activities significantly decreased. Ca2+/Mg2+-ATPase was more sensitive to pressure than Na+/K+-ATPase, and the enzyme activities were almost completely inactivated after pressurization at 500 MPa. High pressure treatment caused obvious damage to the membrane of E. coli O157:H7 cells. The major cause of E. coli O157:H7 death after high hydrostatic pressure treatment was the inactivation of Ca2+/Mg2+-ATPase.

Key words: high hydrostatic pressure, Escherichia coli O157:H7, cell membrane