Gene expression measurements for Salmonella pathogenicity island II. Gene expression measurements for Salmonella Pathogenicity Island II (SPI-II) from Salmonella typhimurium. The genome is represented as two barplots, one for each strand. Each gene has three bars representing expression at 4 h, 8 h and 12 h post macrophage infection. Gene expression measurements (y-axis) are ratios of test RNA to control RNA on the log 2 scale. Distance between genes is relative and representative of intergenic distance. This island has been linked to pathogenicity, and encodes a type III secretion system. It is required for systemic infection and intracellular pathogenesis by facilitating replication of intracellular bacteria within membrane-bound Salmonella-containing vacuoles . Here we can clearly see that the majority of genes in the island are strongly up-regulated during macrophage infection.