EFFECT OF HEAT-SHOCK ON PRODUCTION OF LISTERIOLYSIN-O BY LISTERIA-MONOCYTOGENES

A Listeria monocytogenes serotype 1 strain was examined to determine t he effect of heat shock on production of listeriolysin O (LLO) and the ability of injured cells to resume production of LLO after heat treat ment 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 (R BC). Heat shocking of Listeria cells resulted in almost total reductio n in LLO activity. However, within 4 h of incubation of 37C, heat-shoc ked cells resumed production of LLO, achieving an activity level 40-ti mes higher than that immediately after heat shock. In comparison, in t he same time period there was an increase of only 2-fold in the hemoly tic activity of nonheat-shocked controls. These results provide additi onal evidence, besides increased thermotolerance, of how heat-shock of pathogenic organisms could affect the safety of foods.