Using transcriptional promoter fusions, we investigated the expression of selected SPI-1 and SPI-2 genes of Salmonella enterica serovar Typhimurium (S. Typhimurium). Promoters of genes related to the invasion of the epithelial cell (hilA, hilC, hilD, invF, sicA, sopA, sopB and sopE2) were active in Luria-Bertani (LB) medium and LB with butyrate but were suppressed by bile salts and in glucose minimal (M9) medium. Genes related to S. Typhimurium intracellular survival (phoP, ssrA, ssaB, ssaG, sifA, sifB and pipB) were characterized by their expression in stationary phase in LB and M9 medium. Activity of phoP and ssrA promoters indicated that these might be expressed inside the gut. SPI-1 genes were expressed on the transition to stationary phase while SPI-2 genes were expressed in stationary phase. Among SPI-1 genes, those with regulatory functions preceded in expression the effector genes and sop genes were expressed in the order of sopA, sopB and sopE2, showing hierarchy in the expression of S. Typhimurium virulence genes.

Salmonella enterica subsp. enterica originating from poultry and poultry products is responsible for the vast majority of human gastrointestinal disorders in Europe. For this reason different measures that seek to decrease its incidence in poultry including vaccination with inactivated vaccine continue to be tested. In this study we compared four different inactivated vaccines of S. Typhimurium in chickens which were enriched by SPI-1 or SPI-2 proteins that are central to Salmonella virulence. Six-week-old chickens were intramuscularly vaccinated, revaccinated at 9 weeks and challenged at 12 weeks of age. For two weeks post challenge faecal shedding was monitored. There was no significant difference in the performance of the four compared inactivated vaccines and all of them decreased faecal shedding during the first weeks post infection by 10-1 000× when compared with non-immunized control chickens. However, the level of protection provided by inactivated vaccines was much lower when compared with a live vaccine based on a phoP rpoS double deletion S. Typhimurium mutant which was included as an additional control.