2.+Pathogenicity+(aa397)

Pathogenicity:

Pathogenicity is commonly described as the function of a parasite to cause damage on the host target. Legionella bacteria are an intracellular organism found mainly in watery areas. Legionella is a gram-negative bacterium that spreads through water vapour which when inhaled by a human can lead to the progression of the disease. Legionella can either lead an independent existence or live as a parasite. ref? The bacteria degrades cells which ones? in two phases: by the mediation of cell death and injury during the beginning stages of infection, followed by an independent and intensified cell death during later stages of the infection, stimulated by the formation of pores. explain, expand, reference. Once Legionella enter the host cell the bacteria are known to be able to avoid endosomal and lysosomal activity, however the immune response is quick to react recruiting macrophages to the area of infection due to the expression of the cytokine IL-8 (Interlukin-8) induced by the Legionella bacteria flagellum.” //**Moreover,**// **// Legionella //**//** flagellin seemed to be involved in IL-8 expression, since a **// **// flaA //**//** knockout mutant, defective in flagellin production, failed to induce IL-8 mRNA immediately after the infection **//** ”. ** **__ Mechanisms of Legionella pneumophila-induced interleukin-8 expression in human lung epithelial cells. __** **__ Hiromitsu Teruya et al. ? repetition __** After the expression of il8 the recruitment of the alveolar macrophages induces them to take up the Legionella by phagocytosis. After the Legionella is phagocytosized they ? undergo a physiological transformation, which integrates the Legionella bacteria into part of the phagosomes. The Legionella that have control of the phagosome are now able to freely initiate a secretion system expressed by the Dot ICM gene. The secretion system includes signalling proteins/effectors, which result in averting the overall maturation of the phagosome. One of the signalling proteins expressed by the Legionella is known as cyclic diguanylate, is the regulator of a large number of variably important processes in the Legionella bacteria. These processes include. Motility the independent movement of the Legionella bacteria Bio film formation helps the Legionella bacteria exist independent of a host i n the phagosome?? Cell division the Legionellas ability to proliferate Virulence and Growth. The //Legionella bacteria also express an// effector protein effector proteins secreted by the DOT ICM known as DrrA. This effector protein acts as an exchange factor for guanine nucleotide (GEF) present in Rab1 ( Rab1 being a GTPase that has the ability to regulate the transport of vesicles derived from the endoplasmic-reticulum) ; therefore activating this GTPase causes the aggregation of these vesicles to the area of expression. So? Why is this important? DrrA maintains the active state of Rab1 by a process called Ampylation. This is done by the addition of an adenosine 5'-monophosphate (AMP) to Tyr77 modification that happens after translation mechanism. The small Guanosine Triphosphatase (GTPase) Rab1 is the target for the phagosomes containing Legionella. This targeting results in the recruitment of endoplasmic reticulum derived vesicles. The vesicles surround the Legionella and flatten it until the phagosome fuses with vesicles. Ribosomes are later recruited to the phagosome containing Legionella Once a Legionella is in an endoplasmic derived vesicle it is hidden from the lysosomal activity Now the Legionella cannot be attacked by the lysosomes they multiply freely within the macrophage They grow in the presence of L-cysteine and iron growing flagella becoming mobile and then try to exit the macrophage by cycles of phagocytosis and multiplication



Optimal growth temperature is 28-40°C; organisms are dormant below 20°C and are killed at temperatures above 60°C.

__ Refrences __ 1.Swanson MS, Hammer BK. //Legionella pneumophila // pathogenesis: a fateful journey from amoebae to macrophages. Annu Rev Microbiol. 2000; 54 :567–613. doi: 10.1146/annurev.micro.54.1.567. 2. Jules M, Buchrieser C. Legionella pneumophila adaptation to intracellular life and the host response: clues from genomics and transcriptomics. **//FEBS Lett. 2007 Jun 19;581(15):2829-38.//** 3. [|Benson RF, Fields BS. Classification of the genus Legionella. Semin Respir Infect 1998; 13:90] 4. [|**Cianciotto NP**]. Pathogenicity of Legionella pneumophila. [|**Int J Med Microbiol.**] 2001 Nov;291(5):331-43. 5. Meitz, A. 1988. Microbial life in cooling water systems. ASHRAE J. 30:25-30.

Poor effort, references are missing from the main text, the one figure is already on the wiki, poorly written and in some places it shows poor understanding of the topic