The progeny of Legionella pneumophila in human macrophages shows unique developmental traits


  • Hany Abdelhady,

    Corresponding author
    1. Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada
    • Correspondence: Rafael A. Garduño, Department of Microbiology & Immunology, Dalhousie University, Sir Charles Tupper Medical Building, 7th floor, 1459 Oxford Street, Halifax, NS, Canada B3H 4R2. Tel.: +902 494 6575; fax: +902 494 3889; e-mail:

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  • Rafael A. Garduño

    1. Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada
    2. Department of Medicine-Division of Infectious Diseases, Dalhousie University, Halifax, NS, Canada
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The Gram-negative bacterium Legionella pneumophila is an intracellular parasite of amoebae and an accidental human pathogen that causes a noncommunicable atypical pneumonia known as Legionnaires' disease (LD). In some mammalian cells (e.g. HeLa), L. pneumophila follows a biphasic developmental cycle, differentiating between a replicative form that actively multiplies intracellularly, and a mature infectious form (MIF) that emerges as progeny. To date, it is not known whether the L. pneumophila progenies that emerge from amoebae and human macrophages reach similar developmental stages. Here, we demonstrate that in relation to the fully differentiated and highly infectious MIFs that emerge from amoebae, the L. pneumophila progeny that emerges from macrophages is morphologically undifferentiated, less resistant to antibiotics and less able to initiate infections. However, the L. pneumophila progeny from macrophages did not show any defects in intracellular growth. We thus concluded that macrophage infection with L. pneumophila yields a low number of bona fide MIFs. Because MIFs are the transmissive forms of L. pneumophila produced in vivo, our results showing that they are not efficiently produced in cultured macrophages provide an initial insight into why LD is not communicable.