Growth temperature alters Salmonella Enteritidis heat/acid resistance, membrane lipid composition and stress/virulence related gene expression.

摘要

The influence of growth temperature (10, 25, 37, and 42 degrees C) on the survival of Salmonella Enteritidis in simulated gastric fluid (SGF; pH=2.0) and during heat treatment (54, 56, 58, and 60 degrees C), on the membrane fatty acid composition, as well as on stress-/virulence-related gene expression was studied. Cells incubated at temperatures lower or higher than 37 degrees C did not increase their acid resistance, with the maximum D-value of 3.07 min in cells grown at 37 degrees C; while those incubated at higher temperature increased their heat resistance, with the maximum D_{60 degrees C}-values of 1.4 min in cells grown at 42 degrees C. A decrease in the ratio of unsaturated to saturated fatty acids was observed as the growth temperature increased. Compared to the control cells grown at 37 degrees C, the expression of rpoS was 16.5- and 14.4-fold higher in cells cultivated at 10 and 25 degrees C, respectively; while the expression of rpoH was 2.9-fold higher in those cultivated at 42 degrees C. The increased expression of stress response gene rpoH and the decreased ratio of unsaturated to saturated fatty acids correlated with the greater heat resistance of bacteria grown at 42 degrees C; while the decreased expression of stress response gene rpoS at 42 degrees C might contribute to the decrease in acid resistance. Virulence related genes-spvR, hilA, avrA-were induced in cells cultivated at 42 degrees C, except sefA which was induced in the control cells. This study indicates that environmental temperature may affect the virulence potential of S. Enteritidis, thus temperature should be well controlled during food storage.