Fecal coliforms
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Fecal coliforms are bacteria that ferment lactose to produce acid and gas at 44.5 °C within 24 hours. They include the genera Escherichia and Klebsiella, and have been used as indicator organisms for water quality testing.
Fecal coliforms as indicator of water quality
Fecal coliforms are found in the gut of humans and warm blooded animals. When fecal coliforms are found in water bodies in great quanities, they may indicate a higher risk of pathogens being present in the water. While only a few Enterobacteria are problematic for humans, they serve the purpose of indicating risk of other known pathogens.
Bacteria are single-celled organisms that can only be seen with the aid of a very powerful microscope. Bacteria can be found everywhere - in air, water, and soil, even in and on your own body. They can benefit us by recycling wastes, helping nitrogen-fixing plants to grow, and by making certain types of food. They may harm us by causing diseases and food spoilage. Of environmental concern are the many types of 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. A specific subgroup of this collection is the fecal coliform bacteria, the most common member being Eschericia 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. 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 stream water, we can determine approximately how many bacteria were originally present.
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. Individual home septic tanks can become overloaded during the rainy season and allow untreated human wastes to flow into drainage ditches and nearby waters. Agricultural practices such as allowing animal wastes to wash into nearby streams during the rainy season, spreading manure and fertilizer on fields during rainy periods, and allowing livestock watering in streams can all contribute fecal coliform contamination.
At the time this occurs, the source water may be contaminated by pathogens or disease producing bacteria or viruses, which can also exist in fecal material. 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. While these bacteria do not directly cause disease, high quantities of fecal coliform bacteria suggest the presence of disease causing agents. The presence of fecal contamination is an indicator that a potential health risk exists for individuals exposed to this water. During high rainfall periods, the sewer can become overloaded and over flow, bypassing treatment. As it discharges to a nearby stream or river, untreated sewage enters the river system. Runoff from roads, parking lots, and yards can carry animal wastes to streams through storm sewers.
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.
Testing
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. This test requires a very careful set of sterile procedures, as well as expensive equipment and a five-day test. Less expensive screening techniques are available for use by the trained student.Field kits for fecal coliform are available but expensive. A trained microbiologist is also helpful in conducting proper test procedures.
Untreated fecal material, such as contains fecal coliform, adds excess organic material to the water. The decay of this material depletes the water of oxygen. This lowered oxygen may kill fish and other aquatic life. Reduction of fecal coliform in wastewater may require 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.
Analysis
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 micrometres). 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 20-60 colonies/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 (45 m 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 44.50o 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.
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.
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