Fecal coliforms
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Fecal coliforms (sometimes faecal coliforms) are bacteria that ferment lactose to produce acid and gas at 44.5 °C up to 48 hours. They include the genera Escherichia Enterbacter, bacillus and Klebsiella, and they are used as indicator organisms in water quality testing. Although the bacteria are not pathogenic, they are an early indication of faecal contamination and likely presence of other pathogens. In general, increased levels provide a warning of failure in water treatment, a break in the integrity of the distribution system, or possible contamination with pathogens. When levels are high there may be an elevated risk of waterborne gastroenteritis. Tests for the bacteria are cheap, reliable and rapid.
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[edit] Fecal coliforms as indicator of water quality
[edit] Basics of fecal coliform bacteria
Fecal coliform bacteria are a group of bacteria that are passed through the fecal excrement of humans, livestock and wildlife. They aid in the digestion of food. The most common member type of fecal coliform bacteria is Escherichia coli. These organisms may be separated from the total coliform group by their ability to grow at elevated temperatures and are associated only with the fecal material of warm-blooded animals.
[edit] Potential sources of fecal coliform bacteria in water
The presence of fecal coliform bacteria in aquatic environments indicates that the water has been contaminated with the fecal material of man or other animals. Fecal coliform bacteria can enter rivers through direct discharge of waste from mammals and birds, from agricultural and storm runoff, and from untreated human sewage.
[edit] Human sewage
Failing home septic tanks can allow untreated human wastes to flow into drainage ditches and nearby waters. Sewage connections that are improperly connected to stormwater drainage pipes can also allow human sewage into surface waters. Some older industrial cities, particularly in the Northeast and Midwest of the United States, use a combined sewer system to handle waste. A combined sewer contains both human sewage and stormwater. During high rainfall periods, a combined sewer can become overloaded and overflow to a nearby stream or river, bypassing treatment.
[edit] Pets
Pets, especially dogs, can contribute to fecal contamination of surface waters. Runoff from roads, parking lots, and yards can carry animal wastes to streams through storm sewers.
[edit] Agriculture
Agricultural practices such as allowing livestock to graze near water bodies, spreading manure as fertilizer on fields during rainy periods, and allowing livestock watering in streams can all contribute to fecal coliform contamination.
[edit] Birds
Birds can be a significant source of fecal coliform bacteria. Ducks, geese, seagulls, and other waterfowl can all elevate bacterial counts, especially in wetlands, lakes, and ponds.
[edit] Problems resulting from fecal contamination of water
[edit] Human health hazards
Large quantities of fecal coliform bacteria in water may indicate a higher risk of pathogens being present in the water. Some waterborne pathogenic diseases include ear infections, dysentery, typhoid fever, viral and bacterial gastroenteritis, and hepatitis A. The presence of fecal coliform tends to affect humans more than it does aquatic creatures, though not exclusively.
[edit] Effects on the environment
Untreated organic matter that contains fecal coliform can be harmful to the environment. Aerobic decomposition of this material can reduce dissolved oxygen levels if discharged into rivers or waterways. This may reduce the oxygen level enough to kill fish and other aquatic life. Reduction of fecal coliform in wastewater may require the use of chlorine and other disinfectant chemicals. Such materials may kill the fecal coliform and disease bacteria. They also kill bacteria essential to the proper balance of the aquatic environment, endangering the survival of species dependent on those bacteria. So, higher levels of fecal coliform require higher levels of chlorine, threatening those aquatic organisms.
[edit] Removal and treatment
Fecal coliform, like other bacteria, can usually be killed by boiling water or by treating with chlorine. Washing thoroughly with soap after contact with contaminated water can also help prevent infections. Gloves should always be worn when testing for fecal coliform. Municipalities that maintain a public water supply will typically monitor and treat for fecal coliforms. See more at Water purification.
[edit] Testing
[edit] Public health risk monitoring
In waters of the U.S., Canada and other countries, water quality is monitoried to protect the health of the general public. Bacteria contamination is one monitored pollutant. In the U.S., fecal coliform testing is one of the nine tests of water quality that form the overall water-quality rating in a process used by the EPA. The EPA has approved a number of different methods to analyze samples for bacteria.
[edit] Analysis
Bacteria reproduce rapidly if conditions are right for growth. Most bacteria grow best in dark, warm, moist environments with food. Some bacteria form colonies as they multiply which may grow large enough to be seen. By growing and counting colonies of fecal coliform bacteria from a sample of water, we can determine approximately how many bacteria were originally present.
Membrane filtration is the method of choice for the analysis of fecal coliforms in water. Samples to be tested are passed through a membrane filter of particular pore size (generally 0.45 micrometre). The microorganisms present in the water remain on the filter surface. When the filter is placed in a sterile petri dish and saturated with an appropriate medium, growth of the desired organisms is encouraged, while that of other organisms is suppressed. Each cell develops into a separate colony, which can be counted directly, and the results calculated as microbial density. Sample volumes of 1 ml and 10 ml will be used for the water testing, with the goal of achieving a final desirable colony density range of 20 to 60 colonies per filter. Contaminated sources may require dilution to achieve a "countable" membrane.
A 100 ml volume of a water sample is drawn through a membrane filter (0.45 µm pore size) through the use of a vacuum pump. The filter is placed on a petri dish containing M-FC agar and incubated for 24 hours at 44.5 °C. This elevated temperature heat shocks non-fecal bacteria and suppresses their growth. As the fecal coliform colonies grow they produce an acid (through fermenting lactose) that reacts with the aniline dye in the agar thus giving the colonies their blue color.
The Coli Chrome 2 redigel medium is a new and patented formulation for water testing. It contains a sugar linked to a dye which, when acted on by the enzyme beta-galactosidase, turns the colony a red color. Similarly, there is a second sugar linked to a different dye which, when acted on by the enzyme beta-glucuronidase, turns an E. coli colony a light blue or blue-green color. Because E. coli produces both beta-galactosidase and beta-glucuronidase, the colony grows with a purple color (red + blue). The combination of these two dyes makes possible the unique ability to use one test to differentiate and quantify coliforms and E. coli. Because E. coli is a member of the coliform group, add the number of purple colonies to the number of red colonies when counting coliforms.
The method used in this class (Environmental Science) employs the Coliscan gel method. Colonies, which have the blue or blue-green color, are not exhibiting any beta-galactosidase activity (which is evidenced by the red color). Because of this, they are not considered to be either coliforms or E. coli and therefore should be ignored when counting coliform or E. coli colonies. Colonies that are white are exhibiting neither color-causing enzyme, and should also be ignored.
Colonies on the surface of the plate are exposed to the medium on only the underside of the colony. This causes these colonies to appear with much less of the indicator color. E. coli colonies may only have a slight purple tinge to them, and it may appear only in the center of the colony with the remainder of the colony being white. Coliforms on the surface may be light pink or white with just a bit of red in the center.
[edit] USEPA testing requirements
The new USEPA coliform rule requires major monitoring changes by the drinking water industry. The testing requirements for drinking water are markedly increased. Not only is the number of routine coliform tests increased, especially for the smaller utilities, but also a new regulation requires automatic repeat testing from all sites that show a total coliform positive.
The current USEPA recommendations for body-contact recreation is fewer than 200 colonies/100 mL; for fishing and boating, fewer than 1000 colonies/100 mL; and for domestic water supply, for treatment, fewer than 2000 colonies/100 mL. The drinking water standard is less than 1 colony/ 100 ml.
