Coliform Index
Encyclopedia
The coliform index is a rating of the purity of water
based on a count of fecal
bacteria
. Coliform bacteria
are microorganism
s that primarily originate in the intestines of warm-blooded
animals. By testing for coliforms, especially the well known E.Coli
, which is a thermo tolerant coliform, one can determine if the water has probably been exposed to fecal contamination; that is, whether it has come in contact with human or animal feces. It is important to know this because many disease-causing organisms are transferred from human and animal feces to water, from where they can be ingested by people and infect them. Water that has been contaminated by feces usually contains pathogen
ic bacteria, which can cause disease. Some types of coliforms cause disease, but the coliform index is primarily used to judge if other types of pathogenic bacteria are likely to be present in the water.
The coliform index is used because it is difficult to test for pathogenic bacteria directly. There are many different types of disease-causing bacteria, and they are usually present in low numbers which do not always show up in tests. Thermotolerant coliforms are present in higher numbers than individual types of pathogenic bacteria and they can be tested for relatively easily.
However, the coliform index is far from perfect. Thermotolerant coliforms can survive in water on their own, especially in tropical regions, so they do not always indicate fecal contamination. Furthermore, they do not give a good indication of how many pathogenic bacteria are present in the water, and they give no idea at all of whether there are pathogenic virus
es or protozoa which also cause diseases and are rarely tested for. Therefore, it does not always give accurate or useful results regarding the purity of water.
coliform is gram negative nonsporing facultatively anaeboric bacteria.
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
based on a count of fecal
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. Coliform bacteria
Coliform bacteria
Coliform bacteria are a commonly used bacterial indicator of sanitary quality of foods and water. They are defined as rod-shaped Gram-negative non-spore forming bacteria which can ferment lactose with the production of acid and gas when incubated at 35-37°C...
are microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s that primarily originate in the intestines of warm-blooded
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...
animals. By testing for coliforms, especially the well known E.Coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
, which is a thermo tolerant coliform, one can determine if the water has probably been exposed to fecal contamination; that is, whether it has come in contact with human or animal feces. It is important to know this because many disease-causing organisms are transferred from human and animal feces to water, from where they can be ingested by people and infect them. Water that has been contaminated by feces usually contains pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
ic bacteria, which can cause disease. Some types of coliforms cause disease, but the coliform index is primarily used to judge if other types of pathogenic bacteria are likely to be present in the water.
The coliform index is used because it is difficult to test for pathogenic bacteria directly. There are many different types of disease-causing bacteria, and they are usually present in low numbers which do not always show up in tests. Thermotolerant coliforms are present in higher numbers than individual types of pathogenic bacteria and they can be tested for relatively easily.
However, the coliform index is far from perfect. Thermotolerant coliforms can survive in water on their own, especially in tropical regions, so they do not always indicate fecal contamination. Furthermore, they do not give a good indication of how many pathogenic bacteria are present in the water, and they give no idea at all of whether there are pathogenic virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es or protozoa which also cause diseases and are rarely tested for. Therefore, it does not always give accurate or useful results regarding the purity of water.
See also
- Indicator organismIndicator organismIndicator organisms are used to measure potential fecal contamination of environmental samples. The presence of coliform bacteria, such as E. coli, in surface water is a common indicator of fecal contamination...
coliform is gram negative nonsporing facultatively anaeboric bacteria.