| dc.description | Legionella pneumophila is the facultatively intracellular, Gram negative bacterium that causes Legionnaires' disease. Within its host cell, the alveolar macrophage, L.pneumophila survives and grows because it is able to resist fusion of its phagosome with lysosomes. The mechanism for this is unknown. Intracellular pathogenesis of L.pneumophila was studied (1) by examining L.pneumophila infection in various cell lines, (2) by comparing a virulent (Lp2064) and an isogenic Mueller-Hinton-selected avirulent (Lp2064M) organism for their respective abilities to survive intracellularly, and (3) by examining the protein profiles of intracellular bacteria and comparing them to extracellular responses. Despite a significant range in relative susceptibility, all of the cell lines examined supported L.pneumophila infection. L929 cells were most sensitive, yielding plaques at low multiplicities of infection. Infection of L929 cells (or monocytes) with Lp2064 resulted in the host cells being lysed due to the growth of the virulent organism within phagosomes. In contrast, Lp2064M was killed within phagolysosomes and consequently produced no cytopathic effect. The major difference between the protein profiles of intracellularly-derived Lp2064 or Lp2064M was the overwhelming expression in Lp2064 of the L.pneumophila heat shock protein, Hsp 60. Also characteristic, was the smearing pattern in lanes containing Lp2064M samples. Lp2064 and Lp2064M were found to respond to tissue culture medium (MEM) by differentially synthesizing many proteins including the major outer membrane protein (MOMP). Since the profiles of broth-grown, or agar-grown organisms were identical, it is postulated that the MEM-induced extracellular changes, or alternatively, the intracellularly-induced changes (possibly mediated through Hsp 60) are responsible for affecting the fusion of phagosomes with lysosomes. | en_US |
