P-006. The Impact of Cold Shock Family Proteins (CSPs) in Listeria monocytogenes During Cold Adaptation and Growth at Low Temperatures
Background: Listeria monocytogenes are important food pathogens whose survival and proliferation at low temperatures during refrigerated food storage pose significant food safety challenges. The different possible molecular attributes of psychrotolerance in these organisms are not yet fully understood. Cold shock proteins (CSPs) are small highly conserved nucleic acid binding proteins that are found widely distributed in prokaryotes. Some proteins in this family have been suggested to contribute to various cellular processes including cold stress adaptation mechanisms. The function of CSP homologues encoded by L. monocytogenes cspA, cspB and cspD genes are not yet understood. In this study the role of these CSP homologues in cold adaptation and low temperature growth were investigated. Methods: Real-time quantitative RT-PCR (qRT-PCR) assays were used to monitor csp gene expression changes in response to cold stress exposure of L. monocytogenes. Deletion mutants targeting cspA, cspB and cspD genes were constructed in the L. monocytogenes EGD-e strain background followed by growth evaluation of the mutants in comparison to the parental wild type strain during incubation at 37, 10 and 4 °C. Results: Real-time qRT-PCR analysis revealed significant induction of cspA (6-fold) and cspD (2-fold) gene expressions in response to cold stress exposure of L. monocytogenes. But cspB gene expression was down regulated in response to cold stress. All the csp deletion mutants displayed similar growth pattern to the L. monocytogenes EGD-e wild type strain at 37°C. Meanwhile under cold stress (10°C and 4°C), the cspA null mutant failed to grow, whilst the cspD null mutant growth was significantly impaired in comparison to that of the parental wild type strain. The cspB null mutant on the other hand continued to display similar growth phenotype to the wild type strain under cold stress indicating that its deletion had no influence on L. monocytogenes growth at low temperatures. Conclusions: These results therefore suggest that the L. monocytogenes cspA and cspD genes encode CSP homologues, which are essential for cold adaptation and optimal growth at low temperatures.