Abstract

Salmonella species are intracellular facultative pathogens which survive within phagocytic cells such as macrophages and proliferate inside vacuoles of epithelial cells. Early reports suggested that the capacity for surviving within macrophages was due to the inhibitory effect on the phagosome-lysosome fusion event induced by intracellular Salmonella. However, recent cell biology data, obtained both with phagocytic and epithelial cells, have shown that Salmonella-containing phagosomes have large amounts of lysosomal membrane glycoproteins (lgp), major components of the lysosomal membrane. This apparent discrepancy has partly been clarified at least in epithelial cells: the Salmonella-containing phagosome fuses with lgp-rich compartment different from the classical mature lysosome, as they do not contain certain lysosomal enzymes and are not connected with the endocytic route. Therefore, Salmonella seems to use an alternative strategy not merely based on the inhibition of phagosome-lysosome fusion event. This strategy essentially involves acquisition of only certain lysosomal components to form a specialized phagosomal compartment in which to survive or proliferate intracellularly. These observations have also exemplified the potential use of intracellular bacterial pathogens as biological probes to understand normal biological aspects of the eukaryotic cell. The intracellular lifestyle of Salmonella will undoubtedly provide new insights into the process of lysosome biogenesis.