Variation in resistance to hydrostatic pressure among strains of food-borne pathogens

Among food-borne pathogens, some strains could be resistant to hydrostatic pressure treatment. This information is necessary to establish processing p arameters to ensure safety of pressure-pasteurized foods (N. Kalchayanand, A. Sikes, C. P. Dunne, and B. Ray, J. Food Prot. 61:425-431, 1998). We stud ied variation in pressure resistance among strains of Listeria monocytogene s, Staphylococcus aureus, Escherichia coli O157:H7, and Salmonella species at two temperatures of pressurization.. Early-stationary-phase. cells in 1% peptone solution were pressurized at 345 MPa either for 5 min at 25 degree s C or for 5, 10 or 15 min at 50 degrees C. The viability loss tin log cycl es) following pressurization at 25 degrees C ranged from 0.9 to 3.5 among n ine L. monocytogenes strains, 0.7 to 7.8 among seven S. aureus strains, 2.8 to 5.6 among six E. coli O157:H7 strains, and 5.5 to 8.3 among six Salmone lla strains. The results show that at 25 degrees C some strains of each spe cies are more resistant to pressure than the others. However, when one resi stant and one sensitive strain from each species were pressurized at 345 MP a and 50 degrees C, the population of all except the resistant, aureus stra in was reduced by more than 8 log cycles within 5 min. Viability loss of th e resistant S. aureus strain was 6.3 log cycles even after 15 min of pressu rization. This shows that strains of food-borne pathogens differ in resista nce to hydrostatic pressure (345 MPa) at 25 degrees C, but this difference is greatly reduced at 50 degrees C. Pressurization at 50 degrees C, in plac e of 25 degrees C, will ensure greater safety of foods.