Microbial Pathogenesis Stress Resistance Insights of 65 Listeria Strains: Acidic, Low Temperature, and High Salt Environments

Abstract

Genetically, Listeria monocytogenes is closely related to non-L. monocytogenes (L. innocua, L. welshimeri, L. grayi, L. aquatica, and L. fleischimannii). This bacterium is well known for its resistance to harsh conditions including acidity, low temperatures, and high salt concentrations. This study explored the responses of 65 Listeria strains to stress conditions and characterized the prevalence of stress-related genes. The 65 Listeria strains were isolated from different environments and their viability was assessed in four different tests: independent tests for pH 3, 1 °C, and 5% salt concentration and multiple resistance tests that combined pH 3, 1 °C, 5% salt. From the data, the 65 strains were categorized into stress-resistant (56) or stress-sensitive groups (9), with approximately 4 log CFU/mL differences. The PCR assay analyzed the prevalence of two virulence genes prfA and inlA, and eight stress-related genes: three acid (gadB, gadC, and atpD), two low temperature (betL and opuCA) and three salt resistance genes (flaA, cysS, and fbp). Two low temperature (bet and opuCA) and salt resistance (fbp) genes were more prevalent in the stress-resistant strains than in the stress-sensitive Listeria group.