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Hektoen enteric agar (HEK or HE or HEA) is a selective and differential agar primarily used to recover ''Salmonella'' and ''Shigella'' from patient specimens. HEK contains indicators of lactose fermentation and hydrogen sulfide production; as well as inhibitors to prevent the growth of Gram-positive bacteria. It is named after the Hektoen Institute in Chicago, where researchers developed the agar. ==Use== The definitive use of HEK is to discriminate between ''Shigella'' and ''Salmonella'', although many other species may grow on these plates. However, while the other bacteria may be clinically relevant, the assay does not discriminate among them. Effectively, HEK uses a metabolic assay to divide colonies into "''Salmonella'' and ''Shigella''" and "everything else". Use of these plates assumes that the user is not interested in other enteric pathogens such as ''Klebsiella'' or ''Escherichia''. The plates contain various sugar sources (lactose, sucrose, and salicin), none of which can be used by either ''Shigella'' or ''Salmonella'', but the medium also includes peptone which can be used as a carbon source. Since most bacteria can use the sugars in preference to peptone, these "uninteresting" bacteria acidify the medium and turn a pH indicator yellow or red. Peptone metabolism by ''Shigella'' and ''Salmonella'' alkalises the medium, turning a pH indicator blue. The presence of thiosulfate or ferric ammonium citrate in the medium produces a black precipitate in the presence of H2S, allowing ''Shigella'' – which does not produce H2S, and appears as green colonies – to be distinguished from ''Salmonella'' – which does produce hydrogen sulfide and appears as black colonies.〔Hudzicki, J. "Hektoen Enteric Agar Protocol." (''American Society for Microbiology Microbe Library'' ) retrieved Jan 2013〕 Few sulfur-reducing bacteria exist other than ''Salmonella'', which can be isolated from the intestines. Most of these are inhibited on HEK plates by the inclusion of bile salts, so encountering a black colony that is not ''Salmonella'' is unusual, although not unheard of. Those that are may be identified as red or yellow colonies with a black centre, indicating that they are fermenting sugar and probably not ''Salmonella''. However, rare strains of ''Salmonella'' are capable of lactose fermentation, which will appear in the same way. 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「Hektoen enteric agar」の詳細全文を読む スポンサード リンク
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