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The primary bacterial indicator used for assessment of microbial contamination of water consists of the coliform group. Coliform bacteria are universally present in high numbers in the feces of warm-blooded animals, including humans, and can be detected even after considerable dilution.
Escherichia coli (E. coli), is one of the most common coliform bacteria types. Detection of E. coli is definite evidence of fecal pollution. E. coli are facultatively anaerobic gram-negative rods that live in the intestinal tracts of animals. They can grow in the presence or the absence of oxygen. Under anaerobic conditions, E. coli grow by fermentation, producing mixed acids and gases as end products. They can also grow by anaerobic respiration, utilizing NO3, NO2, or fumarate. This versatility is what gives E. coli its ability to adapt to its intestinal (anaerobic) and its extraintestinal (aerobic or anaerobic) habitats.
As a pathogen, E. coli is best known for its ability to cause intestinal diseases. Five classes of E. coli can result in diarrheal diseases, but three specific pathogenic strains—enterotoxigenic, enteropathogenic, and enteroinvasive—cause problems when present in the water supply. All three of these types can cause acute diarrhea. An outbreak of E. coli-induced diarrhea can have a fatality rate as high as 40 percent in newborn children.
Enterotoxigenic E. coli (ETEC) are an important cause of diarrhea in infants (e.g., in nurseries and institutions), and in travelers to areas with poor sanitation. ETEC are acquired by ingestion of contaminated food and water. Adults in endemic areas develop immunity. In developing countries, children under the age of three experience multiple ETEC infections. The primary symptom of ETEC infection is diarrhea without fever.
Enteroinvasive E. coli (EIEC) penetrate and multiply within epithelial cells of the colon and cause widespread cell destruction. EIEC are very similar to Shigella in their pathogenic mechanisms and the type of clinical symptoms they cause—diarrhea with fever. EIEC infections are endemic in developing countries and are the cause of 1 to 5 percent of diarrheal episodes among people seeking treatment.
Enteropathogenic E. coli (EPEC) are an important cause of traveler's diarrhea in Mexico and in North America. This class of E. coli produces watery diarrhea similar to that of ETEC, probably due to the bacterial invasion of host cells and modification of cellular signals. Diarrheal episodes among children caused by EPEC in endemic populations are normally limited to children under the age of one. In this age group, EPEC causes watery diarrhea with mucus, fever, and dehydration. EPEC is no longer an important cause of infant diarrhea in North America and Europe, but is still a major cause in many developing countries in South America, southern Africa, and Asia.
Escherica coli 0157:H7 is classified by the Centers for Disease Control and Prevention as the cause of one of the emerging infections diseases. E. coli 0157:H7 is one of the more virulent of the many strains of E.coli found in the environment.
MARK G. ROBSON
Author Info: MARK G. ROBSON, The Gale Group Inc., Macmillan Reference USA, New York, Gale Encyclopedia of Public Health, 2002
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