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Chapter 17 : Intracellular Trafficking of Legionella pneumophila within Phagocytic Cells
Category: Microbial Genetics and Molecular Biology; Bacterial Pathogenesis
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A number of bacterial pathogens replicate within macrophages during host infections. Bacteria that establish a novel intracellular route either destroy the nascent phagosomal membrane to gain access to the host cell cytosol or else are targeted to a special membrane-bound compartment that allows exclusion of antimicrobial factors, and presumably access to nutrients. This latter group of pathogens includes Legionella pneumophila, Brucella abortus, Chlamydia species, and the eukaryotic parasite Toxoplasma gondii. The nascent phagosome formed by the coil has a distinct protein composition, an interesting observation likely to be important for subsequent events during intracellular growth. From a number of studies on the behavior of L. pneumophila within phagocytic cells, it is apparent that the phagosome bearing the microorganism is routed within the cell in a fashion distinct from that seen for phagosomes bearing nonpathogens. Protease mutants also appear to have virulences equal to those of wild-type microorganisms, although this result should be interpreted cautiously since partial differences in virulence or histopathology between the mutant and wild type may be difficult to detect in the guinea pig model. At this point, however, it can be said that the protease is dispensable for the intracellular trafficking pathway of L. pneumophila. Perhaps L. pneumophila, by disrupting the phagosomal membrane, causes a series of similar localized changes, with the result that the microorganism is eventually targeted to its replicative niche.