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Chapter 9 : Localization of Legionella pneumophila Mip Protein Inside Phagosomes of Acanthamoeba castellanii
More than 10 years ago, genetic analysis successfully characterized for the first time a virulence-associated gene in Legionella pneumophila. The Mip protein has been shown to contribute to the infection of both protozoa and human macrophages. To get morphological evidence for the virulence association of the Mip protein, the immunogold technique was applied to localize this protein on legionellae before and after invasion of Acanthamoeba castellanii, one of the protozoan species that serve as a natural host in the environment. Mip protein of in vitro cultured legionellae is regularly distributed in the bacterial cell wall/cytomembrane complex. Four hours after uptake of agar-grown legionellae by A. castellanii cells, Mip protein was localized inside phagosomes of the host cells. In the last years, many studies used transmission electron microscopy for demonstrating the sequence of events of the intracellular infection of amoeba with legionellae, as well as the immunogold technique for labeling of host cell proteins such as BiP, which is involved in a chaperoning function of proteins across the membrane of the endoplasmatic reticulum.