Caister Academic Press


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Legionella pneumophila is a Gram-negative facultative intracellular pathogen, which in its natural environment multiplies in protozoa. This bacterium can also cause a severe pneumonia in man, better known as Legionnaires' disease, following infection of alveolar macrophages. L. pneumophila enters its host cell by phagocytosis, creating a phagosome that does not fuse with lysosomes wherein bacteria can multiply. See also: Legionella

Protein Secretion and Virulence in Legionella

When nutrients are depleted, Legionella enters the transmissive phase and expresss virulence proteins, resulting in lysis of host cells and the initiation of a new infection round. In each of these different stages of infection of host cells, virulence proteins need to be transported to their specific place of action. Several protein secretion systems have been identified in L. pneumophila and most of them play an important role in the virulence of this pathogen. Read more at Bacterial Secreted Proteins.

Legionella infect Amoeba

The Legionella bacterium infects free-living amoebae, such as Acanthamoeba, which is abundant in the water supplies and are know to support bacterial growth. In addition, Acanthamoeba cysts are resistant to many disinfectants, which would allow bacteria to survive in the water supplies and they can be air-borne. Acanthamoeba not only harbours Legionella pneumophila but the bacteria also multiply within Acanthamoeba suggesting that bacteria use amoeba both as a host and a reservoir.

Further reading