EFFECT OF REDUCED PH ON SECRETION, STABILITY AND ACTIVITY OF LISTERIA-MONOCYTOGENES LISTERIOLYSIN-O

The effect of environmental parameters on secretion, stability and activity of Listeria monocytogenes listeriolysin O (LLO) was examined. Increasing the initial glucose concentration in proteose peptone medium resulted in reduced LLO activity and lower final pH. Yield of LLO was substantially increased when the medium was buffered with beta-glycerophosphate. Extended storage of active LLO in growth medium adjusted to pH 5.3 resulted in loss of only 10% LLO activity; however, up to 90% activity was lost during storage at pH < 4.5. In contrast, LLO activity was maximal at pH between 4.0 and 5.5. When the initial pH of culture medium was adjusted to give a final pH after growth of 5.3, as little as 10% of the maximum LLO activity was obtained. The results suggest that the degree of acidity may control both secretion and stability of LLO.