The influence of selected preservatives and growth factors on listeriolysin O (LLO) secretion by Listeria monocytogenes was examined. Secretion of LLO was maximal in tryptic soy broth medium. LLO secretion paralleled growth at 10 and 30°C in buffered proteose peptone medium. LLO secretion was supported by a number of carbohydrates and was inhibited by long-chain (P13-18) polyphosphates. Cell yield but not LLO secretion was increased by agitation. Both growth and LLO secretion were inhibited by nitrite, while LLO secretion was selectively inhibited by sorbate and NaCl. These results suggest that LLO secretion is more sensitive than growth to the inhibitory action of preservatives.
Contribution No. 2075 from the Centre for Food and Animal Research.