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. neumophila 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 an feoAB operon lies the feoB gene, which is a ferrous iron transporter and important for intracellular and extracellular growth. The cytochrome-c maturation (ccm) gene promotes iron assimilation and intracellular infection. The iraAB locus is required for virulence, intracellular infection and iron assimilation. Also, the FrgA gene promotes intracellular infection and encodes protein similar to erobactin synthesases. L. pneumophila contain a Type II protein secretion system (T2SS) in addition to the Dot/Icm Type IV secretion system (T4SS). The Lsp (Legionella secretion pathway) system is critical for intracellular growth and virulence.
This mechanism employed by Gram-negative bacteria plays an important role in disease progression of L. pneumophila through the export of toxins, proteases, and other enzymes. T2SS is encoded on five regions scattered over a chromosome and consists of twelve components. The Lps secretion system is also what allows L. neumophila to remain viable under a wide range of environmental conditions by secreting factors that allow the pathogen to persist at low temperatures. Adhesion of microbes is almost always necessary for causing disease because the body can easily flush microbes that lack a firm attachment. Adhesion depends on bindings of specific molecules on both ends; therefore a specific pathogen can only bind to that cell. The presence of pili, liposaccharide, and protein structures at the bacterial surface contribute to initial adhesion to cell surface receptors.
Adhesion is also necessary because often the host cell receptors for bacteria are essential proteins for other functions. Some components of L. pneumophila that assist with adhesion include Type IV pili which generate motile forces, and have external ends that adhere to a solid substrate. Hsp60 is a typical cytoplasmic protein that mediates attachment and invasion. The major outer membrane protein (MOMP) is involved in host-cell recognition and plays an important role in the virulence of L. pneumophila. Question: What laboratory experiments can be used to determine virulence factors being used by a specific pathogen?
Cite this Virulence Factors of Legionella Pneumophila
Virulence Factors of Legionella Pneumophila. (2016, Dec 21). Retrieved from https://graduateway.com/virulence-factors-of-legionella-pneumophila/