Virulence response of a Salmonella Typhimurium hilA:lacZY fusion strain to spent media from pure cultures of selected bacteria and poultry cecal mixed culture

Virulence gene expression in Salmonella is triggered by a variety of environmental factors including changes in the gastrointestinal environment of birds during different dietary regimes. The objective of this study was to determine if growth of specific microorganisms alters the environmental conditions sufficiently to signal Salmonella Typhimurium virulence response. Spent media was obtained from a Salmonella Typhimurium hilA:lacZY fusion strain, a poultry Salmonella Typhimurium strain, Escherichia coli K12, and Lactobacillus caseii. Spent media samples were collected after 2, 4, 8 and 24 h of growth in brain heart infusion broth (BHI) and M9 media. beta-galactosidase assays were performed on the samples to determine virulence expression. Virulence response to Salmonella spent media was 2-fold greater than Lactobacillus spent media at 4, 8 and 24 h growth (P<0.05). Virulence expression almost doubled when exposed to Salmonella Typhimurium (NONA) spent media compared to mixed culture spent media at 4 h, and Salmonella Typhimurium (NONA) was significantly higher than mixed culture spent media at 24 h (P<0.05). Based on these results, it appears that growth of similar bacterial species may alter the composition of rich media sufficiently to influence virulence.