互联网 www.water800.com
	首页	水质标准	水质检测	水质论文	国外水质	水质法规	认证认可
	水质论坛	技术培训	资料下载	留言本	环境保护	卫生监督	水司传真
首页》水质标准　　　　　　　　　　　联系电话：024-23384396　传真：024-23397696

                                2.环境水平和人体摄入

                                3.对人体的影响

                                4.检测方法

                                5.我国供水水质中的水平及国内外标准的限值

                                6.限值

                                7.相关内容

                                8.本站注

                                9.一个参考资料

1.概述

    在水质生物检测方面经常可以看到总大肠菌群、耐热大肠菌群、埃希氏人肠杆菌、推定埃希氏大肠杆菌等术语，日常水质检验中大肠菌群等一般不是分类学的名词。根据国际标准组织ISO9308-1、2：l990(E)附注A大肠菌群、耐热大肠菌群、推定埃希氏大肠杆菌、埃希氏人肠杆菌的定义为：
    1)大肠菌群(Coliform)：革兰氏阴性．无芽胞．氧化酶阴性的杆状菌群．在有胆盐(或其他表面活性剂或具有相似的阻止生长繁殖性能的物质)存在时．能在好氧及兼性厌氧条件下生长繁殖它们在35～37℃条件下培养18h，也能发酵乳糖(及甘露醇)产酸、产气及乙醛。
    2)耐热大肠菌群(Thermotoletant Coliform Organisms)：在44-44.5 ℃温度下具有与大肠菌群相同发酵及生物化学性能的菌群。
    3)推定埃希氏大肠杆菌(Presumptive E.coli)：是耐热大肠菌群中能在色氨酸存在时生成红色吲哚的菌群。
    4)埃希氏大肠杆菌(E. coli)：是指那些推定埃希氏大肠杆菌又在甲基红试验中呈阳性．并能使L-谷氢酸(L-glutamic acid)脱去羧基．但不能产生乙酰甲基甲醇(acetyl-methvl carbinol)．不能利用柠檬酸盐作为唯一的碳源或在氰化钾(KcN)培养基巾不能繁殖的菌种.
    我国习惯将耐热大肠菌群称为“粪大肠菌群”．事实上．耐热大肠菌群中许多种类并非粪便来源，“粪大肠菌群”一词并不合适．容易产牛误导．以为检测出的耐热大肠菌群都是粪便来源的。宋燕燕等泽自世界卫牛组织的《饮用水的质量标准》第二版的第一卷建设性意见(人民卫生出版社．1997)巾也明确指出术语“粪便大肠杆菌群”足不正确的．应该停止使用。
    根据卫牛部“牛活饮用水卫生规范(2001)”36．粪大肠菌群的检测方法．在MFC培养基上生成兰色菌落即为粪大肠菌群．而根据IS0.9308-1：1990(E)．在MFC培养基上牛成兰色菌落即推定为耐热大肠菌群．故国内粪大肠菌群与耐热大肠菌群的检测方法相同。
    此次将“粪大肠菌群”更名为“耐热大肠菌群”，检测方法、检测意义并无改变．只是考虑了后者是同际更通行的名词。
　

1．1基本性质
　

    耐热大肠茼群是总大肠菌群的一部分．将培养温度提高到44～45℃，在此条件下仍能生长和发酵乳糖的菌群被称为耐热大肠菌群。它们由埃希氏菌属以及克雷伯菌属、肠杆菌属和柠檬酸杆菌属中的一些菌种组成。这些生物中．只有埃希氏大肠杆菌(E mf z)是粪源特异性的粪源特异陛就是指通常大量存在于人类、其它哺乳动物和鸟类粪便中，很少在不是粪便污染主体的土壤和水中发现．
    耐热大肠菌群在配水系统中再繁殖是不可能的，除非管网中有充足的营养物质(生化需氧量(BOD)超过10mg／L)或者不合适的物质接触到处理后的水，水温超过15℃，以及管网中没有游离余氯。
　

1．2主要用途
　

    埃希氏大肠杆菌是最准确和专一的粪便污染指示，但检测方法较为复杂。而在大多数情况下耐热性大肠菌群在水中的浓度直接和埃希氏大肠杆菌的浓度相关，所以尽管前者比后者用于指示粪便污染的可靠性相对较差，但前者应用于水质监测被认为是可接受的。检测中使用的国际标准化的方法和培养基是经过认证批准的，也是相对简单且易于获得的。如果必要，耐热大肠菌群的分离菌可进一步验证是否为推定埃希氏大肠杆菌(Presumptive E.coli)。通常情况下，检验其在44±0．5℃下能否使色氨酸产生吲哚是可行的。这些粪源生物或推定埃希氏大肠杆菌的检出和确认，为近期粪便污染提供了强有力的证据而且应立即进行调查。
    另外，通常情况下耐热大肠菌群与总大肠菌群相比，在人和动物粪便中所占的比例较大，而且由于在自然界容易死亡等原因，耐热大肠菌群的存在可认为近期水体直接或间接地受到了粪便污染。因而，与总大肠菌群相比，耐热大肠菌群在水体中的检出，说明水体更为不清洁，存在肠道致病菌和食物中毒菌的可能性更大。WHO也指出，对农村供水来说，总大肠菌群不能作为粪便污染指示物，特别是在热带地区，很多没有卫生学意义的细菌都可出现在供水中，所以必须有其它更准确的粪便污染指示物。而耐热大肠菌群比总大肠菌群更能贴切地反映水体受人和动物粪便污染的程度，且其检测方法比埃希氏大肠杆菌简单得多，易于用一步法检测，应受到重视。
    因此，耐热大肠菌群指标与总大肠菌群指标并不矛盾，它在水处理各个工艺中担任着重要的指示粪源菌去除效率的作用，也用于评估不同质量的水所必须处理的程度以及细菌去除率目标的确定。
　

2.环境水平和人体摄入
　

    耐热大肠菌群在环境中广泛存在。除了埃希氏大肠杆菌，耐热性大肠菌群中的其它属、种还可能源于富营养化的水(如工业废水)或者腐败的植物物质和土壤。在热带和亚热带的水中，耐热性大肠菌群可能在并无明显的人类污染的情况下存在，也可在热带雨林的植物上发现。这就表示耐热性大肠菌群在热带或亚热带的水体中或被有机废弃物富营养化的水中出现并不一定是人类粪便污染，因为它们也可能来源于野生动物，包括鸟类。
    不过动物粪便中也有许多人类病原体，所以在炎热气候下它们在水中出现不能置之不理．一旦它们出现，病原体就可能出现，水处理也可能是不完善的。

3.对人体的影响
　

    耐热大肠菌群同大肠菌群类似，也是水体粪便污染的指示菌，对人体的影响也与大肠菌群类似。
　

4.检测方法
　

    耐热大肠菌群的检测方法可参阅我国《生活饮用水标准检验法-粪大肠菌群》(GB5750-85.37)，卫生部《生活饮用水卫生规范》(2001)附件7生活饮用水检验规范中第37条，以及ISO标准水质分析方法9308-1、-2：1990(E)大肠菌群、耐热大肠菌群、推定埃希氏大肠杆菌的检测和计数。
　

5.我国供水水质中的水平及国内外标准的限值
　

    5．1我国供水水质数据资料
　

    在卫生部《生活饮用水卫生规范》(2001)颁布前．我国只有部分水司对粪大肠菌群进行非常规检测。如深圳水司每月对原水进行一次粪大肠菌群的检测。很少有水司对出厂水和管网水进行粪大肠菌群的检测。故不能提供相关数据。

    5．2国内外标准的限值
   

    我国现行生活饮用水卫生标准GB5749-85中对耐热(粪)大肠菌群未作要求；卫生部生活饮用水卫生规范(2001)中将粪大肠菌群定为每lO0mL不得检出．并规定其为常规检测项目；建设部城市供水行业2000年技术进步发展规划水质目标中将粪大肠菌群限值定为MPN<1/100mL(发酵管法)，膜法则为O个／100mL。
    世界卫生组织(WHO)《饮用水水质准则》中规定对耐热大肠菌群(或E.coli)进行检测，限值为在任l00mL水样中不得检出。他们认为虽然E.coli是更准确的粪型污染的检测指标，但耐热大肠菌群也是可以接受的选择。
    美国EPA未单独对粪大肠菌群作出要求，只是检测包括粪大肠菌群和E.coli在内的总大肠菌群。
    欧盟理事会在98/83/EC中也未对耐热大肠菌群作要求，但要检测E.coli。不过欧盟理事会在80／778／EEC中要求检测粪大肠菌群，限值为MPN<1/100mL(发酵管法)，膜法则为0个/100mL。98／83／EC是在80／778／EEC基础上修改而来的。
    法国生活饮用水水质标准中将耐热大肠菌群的指标定为0个/100mL。
    所以．目前在大多数目家和地区中除美国外只有我国的水质标准还采用“粪大肠菌群”一词，其他大部分国家采用“耐热大肠菌群”的表述。
　

6.限值
　

    考虑到我国以前对粪大肠菌群的检测情况，并参照国内外检测标准，将耐热大肠菌群的限值定为每100mL水样中不得检出。如一旦检出，要立即进行进一步调查。
    前己述及“耐热大肠菌群”与“粪大肠菌群”检测方法相同．为与国际上的命名一致，采用前者。
　

                                                    来源：《城市供水水质标准》检验项目释义

7.相关内容

耐热大肠菌群及检验

大肠埃希氏菌

水中细菌来源与处理

特定底物技术快速检测水中大肠菌群相关指标

8.本站注

   通过互联网的检索，粪大肠菌（fecal coliform）的使用频率要高于耐热大肠菌

9.一个参考资料

A number of bacteria occur naturally in freshwater streams. Some are found living in the water and sediments as photosynthetic autotrophs or a saphrophytes living on dead matter. Others exist in or on other organisms as mutual symbiotes (providing some benefit to the host organisms in exchange for a place to live), commensuals (neither helping nor harming the host), or parasites (utilizing the host in a way that causes harm).

Certain bacteria that live in the intestinal tracts of animals are essential for the recovery of nutrients from digested food. Millions of these naturally occurring organisms are passed out of the body with fecal wastes. If pathogenic (disease-causing) organisms are present, they may be passed as well. When a stream is polluted by fecal material, pathogenic bacteria, viruses, and parasites may be introduced, posing a health hazard to those who come in contact with the water. Municipal and rural water supplies can transmit human diseases such as cholera (Vibrio cholerae), typhoid fever (Salmonella typhi), shigellosis (Shigella), salmonellosis (Salmonella), and gastroenteritis (Campylobacter jejuni, Escherichia coli, Giardia lamblia). The threat of such disease transmission becomes more serious as the population density increases and more sewage pollutes public water supplies, carrying with it human intestinal pathogens.

Rather than test water directly for pathogens, which can be difficult, expensive and even hazardous, researchers use indicator organisms to assess the possibility of fecal contamination. Fecal coliform bacteria, members of the family Enterobacteriacae, which include Escherichia coli , Citrobacter, Enterobacter and Klebsiella species, are often used as indicators. These gram negative bacilli (rod shaped bacteria) are found in the digestive tracts of all warm-blooded animals. Most are not pathogenic. However, because they are eliminated with feces, they are sometimes associated with pathogens such as Vibrio cholera bacteria or a form of Hepatitus virus that is found in the digestive tract. Total coliform bacteria counts are sometimes used to test for water contamination also. These organisms are less precise as fecal contamination indicators because many can live and reproduce in soil and water, without having a human host.

If high numbers of fecal coliform bacteria are found in a sample of stream water, one may conclude that there has been recent fecal contamination, although not necessarily human in origin. Other intestinal bacteria, such as streptococci or enterococci, may have a stronger correlation to human sewage, but no indicator has been identified that is exclusive to humans. The ratio of streptococci to fecal coliform was once thought to determine human versus animal fecal contamination. But, this is no longer though to be reliable because streptococci do not persist long in an open water environment, making it difficult to assess true concentrations. Enterococcal bacteria seem to be consistently associated with human sewage and subsequent diseases, but testing for these organisms involves a lengthy and complicated procedure.

Despite the fact that they can not be linked directly to contamination by human sewage, fecal coliform bacteria counts are often used to regulate surface waters for recreational use, shellfishing, and potability (ability to be safely consumed). Federal regulations stipulate maximun allowable numbers of these bacteria for various uses. If fecal coliform counts are high (over 200 colonies per 100 ml of water sample) in the river or stream, there is a greater chance that pathogenic organisms are also present. A person swimming in such water has a greater chance of getting sick from swallowing disease-causing organisms, or from pathogens entering the body through cuts in skin, the nose, mouth, or the ears. Diseases and illnesses such as typhoid fever, hepatitis, gastroenteritis, dysentery, and ear infections can be contracted in waters with high fecal coliform counts.

Cities and suburbs sometimes contribute human wastes to local rivers through their sewer systems. A sewer system is a network of underground pipes that carry wastewater. In a separate sewer system, sanitary wastes (from toilets, washers, and sinks) flow through sanitary sewers and are treated at the wastewater treatment plant. Storm sewers carry rain and snow melt from streets, and discharge untreated waters directly into rivers. Heavy rains and melting snow wash bird and pet wastes from sidewalks and streets into storm drains. In a combined sewer system, both sanitary waste and storm runoff are treated at a wastewater treatment plant. After a heavy rain, untreated or inadequately treated waste may be diverted into the river to avoid flooding the wastewater treatment plant. To avoid this problem, some cities have built retention basins to hold excess wastewater and prevent untreated waste from being discharged into rivers. Without retention basins, heavy rain conditions can result in high fecal coliform counts downstream from sewage discharge points. That is why it is important to note weather conditions on the days before a fecal coliform measurement.

1. Use a sterile container, of possible, to collect your water sample.
2. If sampling by hand, use gloves and hold the sample bottle or tube near the bottom. Face upstream and plunge the bottle (opening downward) below the water surface, then turn the bottle underwater into the current and away from you (make a sweeping "U" turn under the water). Be careful not to disturb the bottom sediment.
3. Leave a bit of air space at the top of the bottle by pouring out a little water, and replace the lid securely.
4. Avoid sampling the water surface because the surface film often contains greater numbers of fecal coliform bacteria than is represented in the rest of the stream or river. Also, avoid sampling the bottom sediments for the same reason, unless this is what you intend to analyze.
5. It is a good idea to collect several samples from any single location to minimize the variability that comes with sampling for bacteria.
6. If the purpose of your sampling is to test for suspected sources of fecal coliform contamination, then the samples should be taken just downstream from the source of contamination (like the mouth of a storm drain), and other samples should be taken upstream from this for comparison. If you are sampling downstream of a sewage treatment plant, take extra precautions to minimize direct contact with the water. Wash thoroughly with antibacterial soap after sampling. You may also want to check with the sewage treatment plant director to see if the sewage treatment effluent is sanitized (chlorinated or irradiated) before it is introduced to the river.
7. Put your water samples in a cooler on ice. Ideally, you should test your water samples within one hour of collection. If this is not possible, the samples bottles should be stored on ice until you get back to the lab, and then stored in a refrigerator. Samples need to be tested within 6 hours of collection to ensure adequate accuracy. After 6 hours, the probability of bacteria dying off or becoming too stressed to be cultured is greatly increased. If you will not be able to arrange to test your sample within 6 hours, you might want to consider having the instructor or another adult collect water on the morning before the experiment.

"Coliscan" is a type of commercially available bacterial growth media that contains a combination of color producing chemicals and nutrients that result in the growth of colonies of general coliform and fecal coliform bacteria in different colors. A test sample of water is added to the Coliscan media and general coliform bacteria will grow as pink-magenta colonies while E. coli (fecal coliform) will grow as purple colonies, and other bacterial types will grow as non-colored colonies. Many coliforms are normally found in soil and water and do not necessarily indicate the presence of fecal contamination, but E. coli is the primary bacterium in the mammalian (including humans) intestinal tract and its presence in food or water indicates fecal contamination. Therefore, E. coli is the coliform that is used as an indicator for fecal contamination.

The Coliscan media contains two color-producing substrates that are acted upon by the presence of the enzymes galactosidase and glucuronidase to produce pigments of different colors. General coliforms will produce the enzyme galactosidase (by fermenting lactose), and the colonies that grow in the medium will be pink in color. Fecal coliforms (E. coli) produce both galactosidase and glucuronidase and will grow as purple (or purple-blue) colonies in the medium. A count of the number of purple colonies will indicate the number of fecal coliforms per sample. The pink colonies indicate the total number of general coliforms per sample. The combined general coliform and fecal coliform number equals the total coliform number. Any non-colored colonies that grow in the medium are not coliforms, but may be other members of the family Enterobacteriacae.

Sterile collection container (sterile bottle or test tube) with water sample

Sterile pipets or sterile transfer pipets (dropper pipets)

Sterile petri dish

Coliscan Easygel (Micrology Laboratories)

Incubator set at 37° C

1. Label a petri dish with your name and the location of your water sample.
2. Wash your hands with antibacterial soap, then open a bottle of Coliscan Easygel.
3. Use a sterile pipet (or a sterile transfer pipet) to add between 1 and 5 ml of your water sample (the amount of water you add depends on the extent of fecal contamination you think is in the water).
4. Swirl the bottle to mix the water with the Coliscan Easygel.
5. Pour the mixture into a sterile petri dish. Gently swirl the dish to cover the bottom evenly.
6. Allow the petri dish to solidify for about 40 minutes.
7. Incubate the plate upside down (to minimize condensation on the agar surface) at 37° C.
8. Count colonies 24-48 hours later. See "Interpreting Coliscan pour plates" guide to assist you in determining which colonies are fecal coliforms.
9. Colonies should be analyzed further by bacterial staining and microscopy. Do simple stains and gram staining.

NOTE: You may want to include a negative control and a positive control in your experiment. Sterile water may be used for the negative control. Water from a toilet can be used as a positive control. Be sure to use reasonable precaution in collecting this sample!

To look at the total number of bacteria in your water sample, you may repeat this method using "Total Count" Easygel (instead of Coliscan Easygel). Decrease the amount of sample water that you add to the Total Count Easygel (0.1-1.0 ml should be sufficient). The resulting colonies that grow indicate the total number of colony-forming bacteria that are in your sample. These include both coliforms and non-coliforms. These colonies may be tested further, using microscopic staining.