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The genus ''Legionella'' is a pathogenic group of Gram-negative bacteria that includes the species ''L. pneumophila'', causing legionellosis (all illnesses caused by ''Legionella'') including a pneumonia-type illness called Legionnaires' disease and a mild flu-like illness called Pontiac fever.〔 It may be readily visualized with a silver stain. ''Legionella'' is common in many environments, including soil and aquatic systems, with at least 50 species and 70 serogroups identified. The side chains of the cell wall carry the bases responsible for the somatic antigen specificity of these organisms. The chemical composition of these side chains both with respect to components and arrangement of the different sugars determines the nature of the somatic or O antigen determinants, which are essential means of serologically classifying many Gram-negative bacteria. ''Legionella'' acquired its name after an outbreak of a then-unknown "mystery disease" sickened 221 persons, causing 34 deaths. The outbreak was first noticed among people attending a convention of the American Legion—an association of U.S. military veterans. The convention occurred in Philadelphia during the U.S. Bicentennial year in July 21–24, 1976. This epidemic among U.S. war veterans, occurring in the same city as—and within days of the 200th anniversary of—the signing of the Declaration of Independence, was widely publicized and caused great concern in the United States. On January 18, 1977, the causative agent was identified as a previously unknown bacterium subsequently named ''Legionella''. See Legionnaires' disease for full details. == Detection == ''Legionella'' is traditionally detected by culture on buffered charcoal yeast extract (BCYE) agar. ''Legionella'' requires the presence of cysteine and iron to grow, so does not grow on common blood agar media used for laboratory-based total viable counts or on-site dipslides. Common laboratory procedures for the detection of ''Legionella'' in water〔ISO 11731-2:2004 (Water quality -- Detection and enumeration of Legionella -- Part 2: Direct membrane filtration method for waters with low bacterial counts )〕 concentrate the bacteria (by centrifugation and/or filtration through 0.2-μm filters) before inoculation onto a charcoal yeast extract agar containing antibiotics (e.g. glycine, vancomycin, polymixin, cyclohexamide, GVPC) to suppress other flora in the sample. Heat or acid treatment are also used to reduce interference from other microbes in the sample. After incubation for up to 10 days, suspect colonies are confirmed as ''Legionella'' if they grow on BCYE containing cysteine, but not on agar without cysteine added. Immunological techniques are then commonly used to establish the species and/or serogroups of bacteria present in the sample. Although the plating method is quite specific for most species of ''Legionella'', one study has shown that a coculture method that accounts for the close relationship with amoebae may be more sensitive since it can detect the presence of the bacteria even when masked by its presence inside the amoeba. Consequently, the true clinical and environmental prevalence of the bacteria is likely to be underestimated due to false negatives inherent in the current lab methodology. Many hospitals use the ''Legionella'' urinary antigen test for initial detection when ''Legionella'' pneumonia is suspected. Some of the advantages offered by this test are that the results can be obtained in a matter of hours rather than the five days required for culture, and that a urine specimen is generally more easily obtained than a sputum specimen. Disadvantages are that the urine antigen test only detects antigen of ''Legionella pneumophila'' serogroup 1 (LP1); only a culture will detect infection by non-LP1 strains or other ''Legionella'' species and that isolates of ''Legionella'' are not obtained, which impairs public health investigations of outbreaks of LD. New techniques for the rapid detection of ''Legionella'' in water samples are emerging, including the use of polymerase chain reaction and rapid immunological assays. These technologies can typically provide much faster results. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Legionella」の詳細全文を読む スポンサード リンク
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