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

In the present study, Listeria monocytogenes Scott A, V7 and CCRC 14930 were first subjected to heat shock at 45degreesC for 1 h or at 48degreesC for 10 min. Thermal tolerance at 55degreesC 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% H(2)O(2), 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 45degreesC-1 h heat shocked cells of strains Scott A and V7 showed an increased survival after exposure to 55degreesC for 60 min. Meanwhile, survival of the 48degreesC-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 45degreesC for 1 h increased the tolerance of L. monocytogenes to NaCl, ethanol and crystal violet. On the other hand, heat shocking at 48degreesC for 10 min although increased the resistance of L. monocytogenes to NaCl reduced its resistance to H(2)O(2) and crystal violet. (C) 2003 Published by Elsevier Ltd.