Exposure to sub-lethal temperatures induces enhanced heat resistance inListeria monocytogenes

The food industry utilizes a variety of stressors such as heat treatment to inactivate or prevent the multiplication of L. monocytogenes in foods. The aim of this study was to identify the extent to which pre-exposure to sub-lethal temperatures would induce temperature tolerance to 60 °C and result in increased D values.The D value of an avirulent L. monocytogenes strain (4ab No 10) was initially determined in Tryptic Soy Broth at 55 °C, 60 °C and 65 °C. The cells were pre-exposed to sub-lethal heat stress of 46 °C (for 30 and 60 min), 48 °C (for 30 and 60 min) and 50 °C (for 30 and 60 min). Then they were exposed to 60 °C and the D 60 values were calculated. The pre-treatment at sub-lethal temperatures enhanced the D 60 value of the strain from 3.03 min to longer times. The D 60 values increased as a function of pre-treatment time at 46 °C: after 30 min exposure it was 5.24 min, and 16.18 min after exposure to 60 min. Similarly, the D 60 value after 30 min and 60 min exposure at 48 °C was 6.72 min and 14...