Effect of Heat Shock on Production of Listeriolysin O by Listeria Monocytogenes1

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 heat‐shocked 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, heat‐shocked cells resumed production of LLO, achieving an activity level 40–times higher than that immediately after heat shock. In comparison, in the same time period there was an increase of only 2–fold in the hemolytic activity of nonheat‐shocked controls. These results provide additional evidence, besides increased thermotolerance, of how heat‐shock of pathogenic organisms could affect the safety of foods.