COLIFORM BACTERIA IN DRINKING WATER,
IS IT HARMFUL OR HARMLESS?
Written for Indiana University/Purdue University East Campus, Summer 2000.
Copy Right© By Ann Bersbach
The coliform group of bacteria comprises the entire aerobic and facultative anaerobic gram
negative, nonspore-forming rod shaped bacteria that ferment lactose (a sugar) within 48 hours at
35oC. Total coliform includes species that may inhabit the intestine of warm-blooded
animals or occur naturally in soil, vegetation and water. In general, coliform bacteria can be
divided into a fecal and nonfecal group. The fecal coliform can grow at a higher temperature
(44.5oC) than the non-fecal coliform. The selective elevated temperature test is very
valuable in differentiating between fecal and nonfecal coliform groups. This differentiation is
very helpful in determining the source of pollution in water and its remoteness, because the nonfecal
bacteria of the coliform group may survive longer than the fecal bacteria in the hostile environment
provided by the water.
Coliform bacteria are generally considered Harmless, but their presence may be indicative of the presence of
disease-producing organisms (pathogenic), that may be found with them. Therefore coliform bacteria are called
The test for coliform bacteria is used to measure the suitability of water for human use. Many regulatory
agencies are measuring the bacteriological quality of water using the fecal coliform test. This test more
reliably indicates the potential presence of pathogenic organisms than do tests for total coliform group of
organisms. *In a culture, colonies produced by fecal coliform bacteria are blue. The nonfecal coliform colonies
are gray to cream colored.
E. coli Bacteria (Escherichia coli), one species of the coliform group, is a natural inhabitant only of the
intestinal tract of warm blooded animals and is always found in feces. Therefore its presence in water samples
is a definite indication of fecal pollution and the possible presence of enteric (intestinal) pathogens. In
addition some strains of E. coli are pathogenic. **The bacterium E. coli colonies have yellow color in urea
In conclusion, since Escherichia coli apparently are all of fecal origin, fecal coliform and E. coli tests
are used in an attempt to more specifically determine the presence of human wastes in water.
**EPA approved MF-mTEC method for testing E.coli in wastewater. Two additional methods were recently approved for use
in Indiana for E. coli detection and counting in wastewater, Coliscan MFTM -utilizes a two chromogenic substrates
resulting in distinct blue pigmented colonies unique to E. coli. The other method is SM 20th eddition-Method
9223B_ColilertTM. . Utilizes a fluorogenic substrate.
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