Salmonella enterica: living a double life in epithelial cells

Intracellular bacterial pathogens can occupy a membrane-bound vacuole or live freely within the cytosol of mammalian cells. Many studies have shown that the enteric bacterium, Salmonella enterica serovar Typhimurium (S. Typhimurium), is a vacuolar pathogen. Recent data, however, have revealed that within epithelial cells there are subpopulations of vacuolar and cytosolic Salmonella. Release from the Salmonella-containing vacuole leads to transcriptional reprogramming of bacteria and their robust replication in the cytosol. Eventually, epithelial cell death via pyroptosis results in cell lysis, proinflammatory cytokine release and escape of the cytosolic bacteria into the extracellular space, providing a potential mechanism of dissemination. This review focuses on the current understanding of this newly described intracellular population of Salmonella.