<i>Salmonella</i>: strategies for survival

Pathogenic bacteria employ various strategies to survive in their hosts. Salmonellae are transmittable via the fecal–oral route, and after reaching the intestinal lumen, they invade tissue via M cells in Peyer’s patches and encounter phagocytic cells, namely, macrophages that play an important role in host defense. However, despite the various bactericidal mechanisms deployed in macrophages, salmonellae reside and replicate on the basis of their unique pathogenesis which is characterized by formation of phagosomes known as Salmonella-containing vacuoles. This is achieved by delivering virulence factors into the host cells. Salmonella has many pathogenicity islands (Salmonella pathogenicity islands, SPIs) in its genome. Of them, SPI-1 and SPI-2 play crucial roles in the invasion of host cells and intracellular survival.