EFFECT OF HEAT-SHOCK ON PRODUCTION OF LISTERIOLYSIN-O BY LISTERIA-MONOCYTOGENES
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A Listeria monocytogenes serotype 1 strain was examined to determine the effect of heat shock on production of listeriolysin O (LLO) and the ability of injured cells to resume production of LLO after heat treatment at 62C for 10 min. Listeria cells were heatshocked at 48C for 2 h, and hemolytic activity quantified by hemolysis of red blood cell (RBC). Heat shocking of Listeria cells resulted in almost total reduction in LLO activity. However, within 4 h of incubation of 37C, heatshocked cells resumed production of LLO, achieving an activity level 40times higher than that immediately after heat shock. In comparison, in the same time period there was an increase of only 2fold in the hemolytic activity of nonheatshocked controls. These results provide additional evidence, besides increased thermotolerance, of how heatshock of pathogenic organisms could affect the safety of foods. Copyright 1994, Wiley Blackwell. All rights reserved