Purpose: This study aimed to investigate the acid/heat resistance and stress/virulence related gene expression of S. Enteritidis after adaptation to cold or heat conditions.
Methods: S. Enteritidis was cultivated at 10, 25, 37, and 42°C. Adapted cells were subject to simulated gastric fluid (pH 2.0) and thermal treatment (54, 56, 58, and 60°C) to determine their acid/heat resistance. D-values were calculated based on survivor curves. The transcription levels of stress-related genes (rpoS and rpoH) and virulence-related genes (spvR, hilA, sefA, and avrA) of adapted cells were evaluated by real-time PCR. Mean values were compared using ANOVA.
Results: Adaptation of cells at lower or higher temperatures than 37°C did not increase their acid resistance; while adaptation to higher temperatures significantly (P < 0.05) increased their heat resistance. For instance, D60°C-values of cells adapted at 10, 25, 37, and 42°C were 0.3, 0.5, 1.0 and 1.4 min, respectively. The rpoS gene expression was 16.5- and 14.4-fold higher in cells cultivated at 10 and 25°C, respectively; while the rpoH gene expression was 2.9-fold higher in those adapted at 42°C. Virulence related genes-spvR, hilA, avrA-were significantly induced by 6.4-, 5.0-, 2.6-fold in cells cultivated at 42°C, except sefA gene which was induced in cells adapted at 37°C.
Significance: These data suggest that environmental temperature may have a significant impact on the heat resistance and virulence potential of S. Enteritidis, thus temperature should be well controlled during food storage.