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Indicator bacteria are types of bacteria used to detect and estimate the level of fecal contamination of water. They are not dangerous to human health but are used to indicate the presence of a health risk. Each gram of human feces contains approximately ~100 billion () bacteria.〔(【引用サイトリンク】title=Intestinal Microflora )〕 These bacteria may include species of pathogenic bacteria, such as ''Salmonella'' or ''Campylobacter'', associated with gastroenteritis. In addition, feces may contain pathogenic viruses, protozoa and parasites. Fecal material can enter the environment from many sources including waste water treatment plants, livestock or poultry manure, sanitary landfills, septic systems, sewage sludge, pets and wildlife. If sufficient quantities are ingested, fecal pathogens can cause disease. The variety and often low concentrations of pathogens in environmental waters makes them difficult to test for individually. Public agencies therefore use the presence of other more abundant and more easily detected fecal bacteria as indicators of the presence of fecal contamination. == Criteria for indicator organisms== The US Environmental Protection Agency (EPA) lists the following criteria for an organism to be an ideal indicator of fecal contamination: # The organism should be present whenever enteric pathogens are present # The organism should be useful for all types of water # The organism should have a longer survival time than the hardiest enteric pathogen # The organism should not grow in water # The organism should be found in warm-blooded animals’ intestines. None of the types of indicator organisms that are currently in use fit all of these criteria perfectly, however, when cost is considered, use of indicators becomes necessary. == Types of indicator organisms == Commonly used indicator bacteria include total coliforms, or a subset of this group, fecal coliforms, which are found in the intestinal tracts of warm blooded animals. Total coliforms were used as fecal indicators by public agencies in the US as early as the 1920s. These organisms can be identified based on the fact that they all metabolize the sugar lactose, producing both acid and gas as byproducts. Fecal coliforms are more useful as indicators in recreational waters than total coliforms which include species that are naturally found in plants and soil; however, there are even some species of fecal coliforms that do not have a fecal origin, such as ''Klebsiella pneumoniae''. Perhaps the biggest drawback to using coliforms as indicators is that they can grow in water under certain conditions. ''Escherichia coli'' (''E. coli'') and enterococci are also used as indicators. 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「Indicator bacteria」の詳細全文を読む スポンサード リンク
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