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Updated: May 6, 2026
Legionella pneumophila Outer Membrane Vesicles: Isolation and Analysis of Their Pro-inflammatory Potential on Macrophages
Published on: February 22, 2017
The progeny of Legionella pneumophila in human macrophages shows unique developmental traits
Hany Abdelhady1, Rafael A Garduño
1Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada.
Abstract:
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.
Insights
Legionella pneumophila emerging from amoebae develop into infectious forms, but progeny from macrophages are less infectious. This explains why Legionnaires
Area of Science:
- Microbiology
- Cell Biology
- Pathogenesis
Background:
- Legionella pneumophila is a Gram-negative bacterium causing Legionnaires' disease (LD), an atypical pneumonia.
- This bacterium is an intracellular parasite of amoebae and an accidental human pathogen.
- L. pneumophila exhibits a biphasic developmental cycle in mammalian cells, differentiating into replicative and mature infectious forms (MIFs).
Purpose of the Study:
- To investigate whether L. pneumophila progeny emerging from amoebae and human macrophages reach similar developmental stages.
- To compare the infectivity and differentiation status of L. pneumophila progeny from different host cells.
Main Methods:
- Comparative analysis of L. pneumophila progeny morphology and infectivity after replication in amoebae versus cultured macrophages.
- Assessment of antibiotic resistance and intracellular growth capabilities of progeny from different host cells.
Main Results:
- Progeny emerging from amoebae are fully differentiated, highly infectious MIFs.
- Progeny emerging from macrophages are morphologically undifferentiated, less antibiotic-resistant, and less infectious.
- L. pneumophila progeny from macrophages showed no defects in intracellular growth.
Conclusions:
- Macrophage infection yields a low number of bona fide mature infectious forms (MIFs) of L. pneumophila.
- Inefficient production of transmissible MIFs in cultured macrophages offers insight into the non-communicable nature of Legionnaires' disease.
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