Effect of heat shock on thermal tolerance and susceptibility of Listeria monocytogenes to other environmental stresses Original Research Article

In the present study, Listeria monocytogenes Scott A, V7 and CCRC 14930 were first subjected to heat shock at 45°C for 1 h or at 48°C for 10 min. Thermal tolerance at 55°C and survival of the heat shocked as well as non-heat shocked cells of L. monocytogenes in the presence of 25% NaCl, 0.01% crystal violet, 0.1% H2O2, and 18% ethanol were examined. It was found that heat shock response of L. monocytogenes varied with strains, the condition of heat shock treatment and type of subsequent stress. Compared with the non-heat shocked cells, the 45°C-1 h heat shocked cells of strains Scott A and V7 showed an increased survival after exposure to 55°C for 60 min. Meanwhile, survival of the 48°C-10 min heat shocked L. monocytogenes cells, regardless of strain, exhibited no significant difference (p>0.05) with their respective control cells. Generally, heat shocking at 45°C for 1 h increased the tolerance of L. monocytogenes to NaCl, ethanol and crystal violet. On the other hand, heat shocking at 48°C for 10 min although increased the resistance of L. monocytogenes to NaCl reduced its resistance to H2O2 and crystal violet.