EFFECT OF PRE-HEAT AND POST-HEAT SHOCK TEMPERATURE ON THE PERSISTENCEOF THERMOTOLERANCE AND HEAT SHOCK-INDUCED PROTEINS IN LISTERIA-MONOCYTOGENES

The effect of incubation temperature, before and after a heat shock, o n thermotolerance of Listeria monocytogenes at 58 degrees C was invest igated. Exposing cells grown at 10 degrees C and 30 degrees C to a hea t shock resulted in similar rises in thermotolerance while the increas e was significantly higher when cells were grown at 4 degrees C prior to the heat shock. Cells held at 4 degrees C and 10 degrees C after he at shock maintained heat shock-induced thermotolerance for longer than cells held at 30 degrees C. The growth temperature prier to inactivat ion had negligible effect on the persistence of heat shock-induced the rmotolerance. Concurrent with measurements of thermotolerance were mea surements of the levels of heat shock-induced proteins. Major proteins showing increased synthesis upon the heat shock had approximate molec ular weights of 84, 74, 63, 25 and 19 kDa. There was little correlatio n between the loss of thermotolerance after the heat shock and the lev els of these proteins. Thermotolerance of heat shocked and non-heat sh ocked cells was described by traditional log-linear kinetics and a mod el describing a sigmoidal death curve (logistic model). Employing log- linear kinetics resulted in a poor fit to a major part of the data whe reas a good fit was achieved by the use of a logistic model.