COLIFORM BACTERIA
How Could Coliform Bacteria Affect
Water Quality?
What are coliforms?
Coliforms
are bacteria that
are always present in the digestive tracts of animals, including humans, and
are found in their wastes. They are also found in plant and soil material.
The
most basic test for bacterial contamination of a water supply is the test for
total coliform bacteria. Total coliform counts give a
general indication of the sanitary condition of a water supply.
Here's
a look at coliforms in general:
· Total
coliforms include bacteria that are found in the soil, in water that has been
influenced by surface water, and in human or
animal waste.
· Fecal
coliforms are the group of the total coliforms that are considered to be
present specifically in the gut and feces of warm-blooded animals. Because the
origins of fecal coliforms are more specific than the origins of the more
general total coliform group of bacteria, fecal coliforms are considered a more
accurate indication of animal or human waste than the total coliforms.
· Escherichia coli (E. coli) is
the major species in the fecal coliform group. Of the five general groups of
bacteria that comprise the total coliforms, only E. coli is generally not found
growing and reproducing in the environment. Consequently, E. coli is considered
to be the species of coliform bacteria that is the best indicator of fecal
pollution and the possible presence of pathogens.
Are Coliform Bacteria Harmful?
Most
coliform bacteria do not cause disease. However, some rare strains of E. coli,
particularly the strain 0157:H7, can cause serious illness.
Recent
outbreaks of disease caused by E. coli 0157:H7 have generated much public
concern about this organism. E. coli 0157:H7 has been found in cattle,
chickens, pigs, and sheep.
Most
of the reported human cases have been due to eating under cooked hamburger.
Cases
of E. coli 0157:H7 caused by contaminated drinking water supplies are rare.
Water
pollution caused by fecal contamination is a serious problem due to the
potential for contracting diseases from pathogens (disease-causing organisms).
Frequently,
concentrations of pathogens from fecal contamination are small, and the number
of different possible pathogens is large. As a result, it is not practical to
test for pathogens in every water sample collected.
Instead,
the presence of pathogens is determined with indirect evidence by testing for
an "indicator" organism such as coliform bacteria.
Coliforms
come from the same sources as pathogenic organisms.
Coliforms
are relatively easy to identify, are usually present in larger numbers than
more dangerous pathogens, and respond to the environment, wastewater treatment,
and water treatment similarly to many pathogens. As a result, testing for
coliform bacteria can be a reasonable indication of whether other pathogenic
bacteria are present.
A number of
bacteria occur naturally in freshwater streams. Some are found living in the
water and sediments as photosynthetic autotrophs or a saphrophytes living on
dead matter.
Others exist in or
on other organisms as mutual symbiotes (providing some benefit to the host
organisms in exchange for a place to live), commensuals (neither helping nor
harming the host), or parasites (utilizing the host in a way that causes harm).
Certain bacteria
that live in the intestinal tracts of animals are essential for the recovery of
nutrients from digested food. Millions of these naturally occurring organisms
are passed out of the body with fecal wastes.
If pathogenic
(disease-causing) organisms are present, they may be passed as well.
When a stream is
polluted by fecal material, pathogenic bacteria, viruses, and parasites may be
introduced, posing a health hazard to those who come in contact with the water.
Municipal and
rural water supplies can transmit human diseases such as cholera (Vibrio
cholerae), typhoid fever (Salmonella typhi), shigellosis (Shigella),
salmonellosis (Salmonella), and gastroenteritis (Campylobacter jejuni,
Escherichia coli, Giardia lamblia).
The threat of such
disease transmission becomes more serious as the population density increases
and more sewage pollutes public water supplies, carrying with it human
intestinal pathogens.
Rather than test
water directly for pathogens, which can be difficult, expensive and even
hazardous, researchers use indicator organisms to assess the possibility of fecal
contamination.
Fecal coliform
bacteria, members of the family Enterobacteriacae, which include Escherichia
coli, Citrobacter, Enterobacter and Klebsiella species, are often used as
indicators.
These gram
negative bacilli (rod shaped bacteria) are found in the digestive tracts of all
warm-blooded animals. Most are not pathogenic.
However, because
they are eliminated with feces, they are sometimes associated with pathogens
such as Vibrio cholera bacteria or a form of Hepatitus virus that is found in
the digestive tract.
Total coliform
bacteria counts are sometimes used to test for water contamination also. These
organisms are less precise as fecal contamination indicators because many can
live and reproduce in soil and water, without having a human host.
If high numbers of
fecal coliform bacteria are found in a sample of stream water, one may conclude
that there has been recent fecal contamination, although not necessarily human
in origin.
Other intestinal
bacteria, such as streptococci or enterococci, may have a stronger correlation
to human sewage, but no indicator has been identified that is exclusive to
humans.
The ratio of
streptococci to fecal coliform was once thought to determine human versus
animal fecal contamination. But, this is no longer though to be reliable
because streptococci do not persist long in an open water environment, making
it difficult to assess true concentrations.
Enterococcal
bacteria seem to be consistently associated with human sewage and subsequent
diseases, but testing for these organisms involves a lengthy and complicated
procedure.
Despite the fact
that they cannot be linked directly to contamination by human sewage, fecal
coliform bacteria counts are often used to regulate surface waters for
recreational use, shellfishing, and potability (ability to be safely consumed).
If fecal coliform
counts are high (over 200 colonies per 100 ml of water sample) in the river or
stream, there is a greater chance that pathogenic organisms are also present.
A person swimming
in such water has a greater chance of getting sick from swallowing
disease-causing organisms, or from pathogens entering the body through cuts in
skin, the nose, mouth, or the ears.
Diseases and
illnesses such as typhoid fever, hepatitis, gastroenteritis, dysentery, and ear
infections can be contracted in waters with high fecal coliform counts.
RELATED
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- Escherichia Coli, E. Coli
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PURICARE
INDUSTRIAL
ENTERPRISES
Water
Treatment
Systems
Ultraviolet Bactericidal System
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