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 sórbate (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. Copyright ©, International Association of Milk, Food and Environmental Sanitarians.