Listeriolysin O Secretion by Listeria monocytogenes in Broth Containing Salts of Organic Acids

Abstract

Antilisterial effects of salts of organic acids have been documented, but there is little information on listeriolysin O (LLO) secretion in the presence of these salts during aerobic and anaerobic incubation. LLO secretion and populations of Listeria monocytogenes were studied in broth containing potassium sorbate (0.05 to 4%), sodium lactate, citrate, acetate, or propionate (0.1 to 8%) after aerobic or anaerobic incubation for 24 h at 35 and 20°C. The order of the antilisterial effects of the salts was propionate > sorbate > acetate > lactate > citrate. Cell proliferation was suppressed during incubation under anaerobic conditions but LLO secretion was enhanced. Citrate, acetate, and lactate enhanced LLO secretion during incubation at 35°C, whereas sorbate suppressed it. Overall, effects of the acids at 20°C were similar to those observed at 35°C, but only acetate and citrate enhanced LLO secretion. The observation that salts of specific organic acids enhance LLO secretion may suggest increased virulence of L. monocytogenes. Combinations of sorbate, an LLO blocking agent, with propionate or lactate, which inhibit proliferation of L. monocytogenes, may prolong the shelf life and increase the safety of foods.