Purpose: Therefore, the objective of this study was to evaluate the effect of sodium chloride on thermal resistance and Caco-2 cell invasion of Salmonella.
Methods: Ten strains of Salmonella were inoculated in tryptic soy broth (TSB) at 35°C for 24 h. The cells were then challenged to 60°C for 1 h, and survivals were enumerated on tryptic soy agar (TSA). Salmonella cells were also examined for Caco-2 cell invasion. Two strains of Salmonella were then selected for the highest thermal resistance/Caco-2 cell invasion efficiency (Salmonella Enteritidis NCCP10812) and the lowest antibiotic resistance/biofilm formation (Salmonella Enteritidis NCCP12243). Two strains were subjected to TSB plus 0, 2, and 4% NaCl for 24 h at 35°C, or exposed to sequentially increased NaCl concentrations up to 4% NaCl. Subsequently, the cells were challenged to 60°C for 1 h and inoculated on to Caco-2 cells. Salmonella cells were then recovered on TSA.
Results: S. Typhimurium NCCP10812 showed increased thermal resistance (P < 0.05) as sodium chloride concentration increased. However, the thermal resistance of the pathogen was not increased by sequential increase of NaCl concentration. Regarding Caco-2 cell invasion efficiency, the invasion efficiency of S. Typhimurium NCCP10812 was not increased, but the efficiency of S. Enteritidis NCCP12243 was increased (P < 0.05) as sodium chloride concentration increased. Moreover, S. Enteritidis NCCP12243 had increased Caco-2 cell invasion efficiency (P < 0.05) by sequential increase of sodium chloride concentration.
Significance: These results indicate that sodium chloride in food may increase thermal resistance and cell invasion efficiency of Salmonella.