Gene expression analysis of Salmonella enterica SPI in macrophages indicates differences between serovars that induce systemic disease from those normally causing enteritis.

Global gene expression of the invasive Salmonella serovars S. Enteritidis and S. Typhimurium, and the less-invasive S. Infantis and S. Hadar was studied during infection of a chicken macrophage cell line. Major functional gene groups responsible for intracellular physiological changes were regulated similarly in all four serovars. However, SPI1 and SPI4 genes of S. Enteritidis and S. Typhimurium were strongly repressed in the macrophages whereas S. Infantis, S. Hadar and other similar serovars maintained up-regulation of these gene sets. This phenomenon may explain some of the biological differences between invasive and non-invasive Salmonella serovars.