Phenotypic heterogeneity and pathogenicity of Listeria monocytogenes under complex salinities of bile salts and sodium salts stress

Listeria monocytogenes is a foodborne pathogen that is widespread in the environment and food, and can cause zoonotic diseases. Previous studies have explored its growth under various environmental stressors, but little is known about its behavior under the complex effects of bile salts and sodium salts. Therefore, this study aimed to explore the differences of different salinities (Brain Heart Infusion (BHI) and BHI medium with 0.90% NaCl, 0.50% NaCl + 0.04% bile salts, and 0.90% NaCl + 0.04% bile salts) on growth, motility, biofilm formation, and virulence of L. monocytogenes. This study also artificially simulated L. monocytogenes contamination in pork samples. The results showed that the maximum specific growth rate (μ_max) of 40 L. monocytogenes isolates was significantly reduced and the lag time (LT) was significantly prolonged under the complex salinity treatment, exhibiting greater growth heterogeneity; serotype 4b isolates exhibited strong resistance under complex salinities. L. monocytogenes biofilm formation was significantly reduced with the increase in complex salinities, motility was inhibited, and pathogenicity was enhanced, especially in serotype 1/2c isolates. Furthermore, the complex salinities also caused damage to the cell membrane of L. monocytogenes. L. monocytogenes grew wildly in pork samples, while its growth was inhibited when bile salts were added to form the complex salinities environment. These results highlight the phenotypic heterogeneity and pathogenicity of L. monocytogenes under complex salinities, offering insights for better risk assessment and pathogen control in food safety.