Influence of ethanol adaptation on Salmonella enterica serovar Enteritidis survival in acidic environments and expression of acid tolerance-related genes

摘要

Cross-protection to environmental stresses by ethanol adaptation inSalmonellaposes a great threat to food safety because it can undermine food processing interventions. The ability ofSalmonella entericaserovar Enteritidis (S.Enteritidis) to develop acid resistance following ethanol adaptation (5% ethanol for 1 h) was evaluated in this study. Ethanol-adaptedS. Enteritidis mounted cross-tolerance to malic acid (a two-fold increase in minimum bactericidal concentration), but not to acetic, ascorbic, lactic, citric and hydrochloric acids. The population ofS. Enteritidis in orange juice (pH 3.77) over a 48-h period was not significantly (p > 0.05) influenced by ethanol adaptation. However, an increased survival by 0.09–1.02 log CFU/ml was noted with ethanol-adapted cells ofS. Enteritidis compared to non-adapted cells in apple juice (pH 3.57) stored at 25 °C (p < 0.05), but not at 4 °C. RT-qPCR revealed upregulation of two acid tolerance-related genes,rpoS(encoding σS) and SEN1564A (encoding an acid shock protein), following ethanol adaptation. The relative expression level of the acid resistance genehdeBdid not change. The resistance phenotypes and transcriptional profiles ofS. Enteritidis suggest some involvement ofrpoSand SEN1564A in the ethanol-induced acid tolerance mechanism.