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Aeromonas salmonicida
''Aeromonas salmonicida'' is a pathogenic bacterium that severely impacts salmonid populations and other species. It was first discovered in a Bavarian brown trout hatchery by Emmerich and Weibel in 1894.〔(【引用サイトリンク】url= http://aqua.merck-animal-health.com/diseases/furunculosis/productadditional_127_113308.aspx. )〕 ''Aeromonas salmonicida’s'' ability to infect a variety of hosts, multiply, and adapt, make it a prime virulent bacterium. ''A. salmonicida'' is an etiological agent for furunculosis, a disease that causes septicemia, haemorrhages, muscle lesions, inflammation of the lower intestine, spleen enlargement, and death in freshwater fish populations. It is found worldwide with the exception of South America.〔Merck Animal Health. (2009). The Disease. Available: http://aqua.merck-animal-health.com/diseases/furunculosis/productadditional_127_113308.aspx. Last accessed 11/06/2011.〕 The major route of contamination is poor water quality; however, it can also be associated stress factors such as overcrowding, high temperatures, and trauma. Spawning and smolting fish are prime victims of furunculosis due to their immunocompromised state of being.
== Morphology and bacterial characteristics ==
''Aeromonas salmonicida'' is a Gram-negative, facultatively anaerobic, nonmotile bacterium. It is rod-shaped, about 1.3-2.0 by 0.8-1.3 mm in size, and grows optimally at temperatures between 22 and 25°C.〔 The bacterium readily ferments and oxidizes glucose, and is catalase- and cytochrome oxidase-positive.
Its molecular properties include a special surface protein array called the A-layer, which is believed to be responsible for the bacterium’s virulent traits, and lipopolysaccharide, the cells' major cell envelope antigen. The A-layer consists of a 50-kD protein, and provides protection to the bacterium. The lipopolysaccharide consists of three moieties: lipid A, a core oligosaccharide, and an ''O''-polysaccharide (O-antigen). The extracellular products of ''A. salmonicida'' consist of 25 proteins, enzymes, and toxins, and many more.〔 In addition, the genome is composed of a single circular chromosome (4,702,402 bp), with two large and three small plasmids. The chromosome yields 58.5% of G+C pairs, has 4086 encoding proteins, and totals 4388 genes.
''A. salmonicida'' isolates flourish when grown on blood agar or tyrosine. Large colonies are observed along with a brown diffusible pigment within two to four days. Most typical strains are morphologically and biochemically homogenous with a few exceptions. Some of these exceptions include a distinguishable variation in pigment production, the bacterium’s ability to ferment selected sugars, and Voges-Proskauer assay results.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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