Virulence protein export systems in Salmonella and Shigella: a new family or lost relatives?

A number of Gram-negative bacterial pathogens secrete 'virulence determinants' directly into the extracellular medium, where they interact with host cells to promote disease. The study of the secretion machinery used by these organisms to transport specific virulence determinants out to the cell surface and beyond is of growing importance in the field of bacterial pathogenesis. Elements of the secretion machinery are shared by several pathogens. These homologous elements may lead to a better understanding of how the machinery works, but the unique elements will tell us more about what distinguishes one bacterial pathogen from another.