Effect of lysozyme or nisin on survival of some bacteria treated with high pressure at subzero temperature

The aim of this work was to examine the inactivation of some Gram-positive and Gram-negative bacteria exposed to the pressure of 193 MPa at -20 °C in the presence of lysozyme or nisin at concentration of 400 µg/ml. The highest effect of pressure at subzero temperature and lysozyme was found with pressure sensitive Pseudomonas fluorescens; viable cells of this strain were not detected in 1 ml of sample after combined treatment. The action of pressure at subzero temperature and lysozyme or nisin against Escherichia coli led to synergistic reduction by 0.7 or 1.6 log cycles, respectively, while it was practically insignificant for two Staphylococcus aureus strains. Viability loss of E. coli and S. aureus occurred during storage for 20 h of the samples at 37 and 5 °C, which were previously pressurized with lysozyme or nisin. The synergistic effect of pressure and nisin at pH 5 against E. coli cells just after the pressure treatment was lower than that at pH 7, however, the extent of the lethal effect after storage was higher.