A Comparison of Salmonella enterica Serovars: Are Prevalence, Virulence and Responses to Environmental Conditions Serovar or Strain Dependent?

Salmonella are considered the leading cause of foodborne illnesses with frequent outbreaks in United States. While more than 2500 serovars have been identified, Salmonella Typhimurium and Salmonella Enteritidis are primarily responsible for most human infections while Salmonella Kentucky and Salmonella Heidelburg are currently the most prevalent serovars associated with poultry contamination. The relationship between virulence and prevalence is not fully understood, but may be a result of environmental stress exposure such as acid stress. In this research, organic acid (acetate) and inorganic acid (hydrogen chloride) were applied to 15 different serovars isolated from human infections or poultry. The growth curves and pH changes were graphed over time. In addition, the virulence gene hilA which regulates the pathogenesis of Salmonella were evaluated using real-time PCR at four different time points, 0, 2, 4, and 24 hours after Salmonella was exposed to two different acids individually. We found: 1) growth of Salmonella and the changes of pH were inversely related; 2) the greatest changes of hilA gene expression occurred between 0 and 2 hours; 3) the expression of hilA was serovar and strain dependent; and 4) hydrogen chloride had a greater impact on hilA gene expression than acetate did. Our study gives a better understanding of the hilA pathway used by Salmonella. At the same time, the effect of environmental stimuli on each serovar was revealed. Differences between serovars were unveiled by comparing the responses to acids as well.