Evidence for pore-forming ability by Legionella pneumophila

Authors

  • James E. Kirby,

    1. Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA.,
    2. Department of Pathology, Massachusetts General Hospital, Boston, MA, USA.,
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  • Joseph P. Vogel,

    1. Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA.,
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  • Helene L. Andrews,

    1. Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA.,
    2. Tufts University School of Veterinary Medicine, Boston, MA, USA.
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  • Ralph R. Isberg

    1. Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA.,
    2. Howard Hughes Medical Institute.,
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Ralph R. Isberg, Department of Molecular Biology and Microbiology, Tufts University School of Medicine. E-mail risberg@opal.tufts.edu; Tel. (617) 636 7393; Fax (617) 636 0337.

Abstract

Legionella pneumophila is the cause of Legionnaires' pneumonia. After internalization by macrophages, it bypasses the normal endocytic pathway and occupies a replicative phagosome bound by endoplasmic reticulum. Here, we show that lysis of macrophages and red blood cells by L. pneumophila was dependent on dotA and other loci known to be required for proper targeting of the phagosome and replication within the host cell. Cytotoxicity occurred rapidly during a high-multiplicity infection, required close association of the bacteria with the eukaryotic cell and was a form of necrotic cell death accompanied by osmotic lysis. The differential cytoprotective ability of high-molecular-weight polyethylene glycols suggested that osmotic lysis resulted from insertion of a pore less than 3 nm in diameter into the plasma membrane. Results concerning the uptake of membrane-impermeant fluorescent compounds of various sizes are consistent with the osmoprotection analysis. Therefore, kinetic and genetic evidence suggested that the apparent ability of L. pneumophila to insert a pore into eukaryotic membranes on initial contact may play a role in altering endocytic trafficking events within the host cell and in the establishment of a replicative vacuole.

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