Fecal coliforms

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Fecal coliforms (sometimes faecal coliforms) are facultatively-anaerobic, rod-shaped, gram-negative, non-sporulating bacteria. They are capable of growth in the presence of bile salts or similar surface agents, oxidase negative, and produce acid and gas from lactose within 48 hours at 44 ± 0.5ºC. The fecal coliform assay should only be used to assess the presence of fecal matter in situations where fecal coliforms of non-fecal origin are not commonly encountered.[1]

Fecal coliforms include the genera that originate in feces; Escherichia as well as genera that are not of fecal origin; Enterobacter, Klebsiella, and Citrobacter. The assay is intended to be an indicator of fecal contamination, or more specifically E. coli which is an indicator microorganism for other pathogens that may be present in feces. As recently as April 2006, many official websites including that of the Environmental Protection Agency failed to address the fact that presence of fecal coliforms does not necessarily indicate the presence of feces.[1]

Fecal coliforms as indicator of water quality

Basics of fecal coliform bacteria

In general, increased levels of fecal coliforms 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 (2 -day incubation).

Potential sources of fecal coliform bacteria in water

The presence of fecal coliform bacteria in aquatic environments may indicate 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. However their presence may also be the result of plant material, and pulp or paper mill effluent.[1]

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.

Animals

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. Birds can be a significant source of fecal coliform bacteria. Swans, geese, seagulls, and other waterfowl can all elevate bacterial counts, especially in wetlands, lakes, and ponds.

Agriculture

Agricultural practices such as allowing livestock to graze near water bodies, spreading manure as fertilizer on fields during dry periods, and allowing livestock watering in streams can all contribute to fecal coliform contamination.

Problems resulting from fecal contamination of water

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.

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.

Removal and treatment

Fecal coliform, like other bacteria, can usually be killed by freezing 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 monitored 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.

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.

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 100 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.

References

  1. 1.0 1.1 1.2 Doyle, M. P., and M. C. Erickson. 2006. Closing the door on the fecal coliform assay. Microbe 1:162-163.

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