ABSTRACT
The Yersinia genus contains three pathogenic species: Y. pestis, the agent of plague, and two enteropathogens, Y. pseudotuberculosis and Y. enterocolitica, which are generally acquired after ingestion of contaminated food. Although these three pathogens have different entry routes and cause different diseases, they share a common tropism for the lymphoid tissues where they resist the host innate immune system. This capacity is essentially conferred by a 70-kb plasmid that is conserved among the three species and is required for virulence. This plasmid, called pYV, encodes the Yop virulon that consists of a complete type III secretion (TTS) system, called Ysc-Yop (reviewed by Cornelis, 2002a; Cornelis, 2002b; Cornelis et al, 1998) (Figure 1). TTS is a highly sophisticated virulence mechanism used by several Gram-negative bacteria that are pathogenic for animals or plants, or symbionts for plants and insects (reviewed by Cornelis and Van Gijsegem, 2000). By this mechanism, bacteria that are either extracellular or localized in phagosomes communicate with eukaryotic cells by injecting bacterial proteins into the
cytosol of these cells. The proteins not only are secreted across the two bacterial membranes but are also translocated across the eukaryotic cell membrane. Inside the eukaryotic cell, these bacterial proteins will subvert and disrupt host cell signaling pathways to the benefit of the pathogenic bacteria.
