Virulence Factors of Legionella Pneumophila

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Biol 228
Virulence factors of Legionella pneumophila

The Gram-negative bacterium Legionella pneumophila contains a singular monopolar flagellum which is composed of a major subunit, the FlaA protein. Motility is associated with the infectious phase of L. pneumophila. In the initial phase, the replicative phase, the bacteria are immotile and have nonexistent or low toxicity. The growth of flagella leads to the infectious phase, where the new motile form of L. pneumophila is highly toxic and much more infectious to its host. Flagellum of L. pneumophila promotes infection by facilitating the encounter of a host cell and increasing invasion capacity. This motility is also needed to locate a new host cell after its release from the spent one. Flagella also give L. pneumophila the ability to respond to environmental factor which aide in its survival. L. pneumophila implements a type IV secretion system known as the Dot/Icm system. This secretion system injects effector proteins into the host which increase the bacteria’s ability to survive within a host cell. L. pneumophila protects against lysis by using its effector proteins to obstruct the fusion of the Legionella-containing vacuole (LVC) with the hosts’ endosomes. The Dot/Icm system is essential for induction of apoptosis in human macrophages. Another role of this system is to inhibit phago-lysosome fusion through the exportation of virulence factors. Research shows that macrophages that have been treated with an iron chelator do not support the replication of L. pneumophila. This demonstrates that iron is crucial for L. pneumophila virulence and replication. The importance of iron acquisition has caused L. pneumophila to develop several mechanisms to acquire iron from its surroundings. L. pneumophila may produce a siderophore as a means to obtain iron during certain phases of growth under iron limiting conditions. The siderophore, known as legiobactin, is an iron chelator. Within...
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