Immunolocalization of the Mip protein of intracellularly and extracellularly grown Legionella pneumophila

The macrophage infectivity potentiator (Mip) protein is an important factor in the optimal intracellular survival of Legionella pneumophila in protozo a and human cell lines. In this study we have localized the Mip protein in Legionella grown on buffered charcoal yeast extract (BCYE) agar as well as in Legionella which were ingested by Acanthamoeba castellanii. Immunogold t echniques have shown that Mip is exposed on the cell surface of extracellul arly grown bacteria. In A. castellanii infected with Legionella the Mip pro tein was also detected on host membranes which exhibited a multilamellar st ructure. The morphology of these structures is similar to that of respirabl e vesicles of amoebas by which live legionellas may be transmitted to human s. It can be assumed that the accumulation of Mip protein in the multilamel lar host membranes increases the infection potential.