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| Michigan Water Science Center |
Fecal Indicator Bacteria and Sanitary Water Quality
Microorganisms are found everywhere in our environment. They are common in
the air, soil, water and in the habitats of our daily lives. The vast
majority of microorganisms do not cause disease. Instead, they maintain the
fertility of soil, they degrade wastes in our landfills and compost piles, and
they cleanse water of the pollutants we add. We purposefully use some
microorganisms to make food (cheese, beer, sauerkraut), we put
microorganisms to work in sewage treatment plants, and we use them in
biotechnology to produce chemicals.
Naturally some microorganisms have learned to live on or in the human body.
Many of these microorganisms do no harm, and are even beneficial because
they compete with other microorganisms that might cause disease if they
could become established in or on our bodies. The fecal indicator bacteria
are such microorganisms; they are normal inhabitants of the gastrointestinal
tract of humans and many other warm-blooded animals and in general, they cause
no harm.
A few microorganisms (called pathogens) can cause disease in humans. In order
to cause disease, a pathogen must successfully invade some part of the body
and either produce more of itself or produce a chemical (usually called a
toxin) which interferes with normal body processes. Whether or not a pathogen
is successful in causing disease is related to the health of the individual
and the state of his or her immune system, as well as to the number of
pathogen cells required to make the person ill. Some pathogens can cause
disease when only a few cells are present. In other cases, many cells are
required to make a person ill. Children and elderly persons are more
susceptible to many pathogens than are young or middle-aged adults.
Some pathogens live out their lives in the soil and water and only cause
disease under unusual circumstances. The microorganism that causes tetanus is
an example. This microorganism (a bacterium named Clostridium tetani) lives
normally in the soil. Clostridium tetani grows in the body only in deep
puncture wounds where air cannot penetrate (termed anaerobic). In this
environment it produces a toxin which spreads throughout the body and may
cause paralysis. Other pathogens are more closely associated with humans and
other warm-blooded animals. These pathogens are transmitted from one organism
to another by direct contact, or by contamination of food or water. Many
of the pathogens which cause gastrointestinal disease are in this category.
Several human gastrointestinal pathogens produce toxins which act on the small
intestine, causing secretion of fluid which results in diarrhea. In severe
cases, such as cholera, the afflicted person may die from loss of body
fluids and severe dehydration. Cells of the pathogen are shed in the feces,
and if these cells contaminate food or water which is then consumed by another
person, the disease spreads.
It is not unusual to find some fecal indicator bacteria and even some
pathogens in natural environments. The organism called Giardia lamblia (a
protozoan) is an example. This organism is found in the gastrointestinal
system of some wild mammals, and may enter water through the feces of these
mammals. The organism causes severe diarrhea in humans. Persons who backpack
or hike in wilderness areas are advised to treat all water before drinking,
even if it comes from a pristine, clear, cold mountain stream. Therefore,
the risk of disease is not uniquely a result of the presence of human wastes
in the environment.
Nevertheless, in natural environments, organisms are relatively dispersed,
therefore wastes are also relatively dispersed. In addition, natural wastes
are composed of compounds natural to that environment and microorganisms in
the soil and water can degrade those wastes and recycle them into usable
forms. When the quantity or type of waste exceeds the capacity of the
microorganisms in soil and water to degrade it, we call the waste
pollution. The degradation capacity of microorganisms in soil and water is
challenged by extreme amounts of wastes, as well as by unusual (often man-
made) or toxic compounds. It is difficult to live in an industrialized and
urbanized world and not produce localized concentrations of wastes. When
human fecal wastes are concentrated in the environment, we assume, for our own
protection, that the risk of transmission of pathogens may increase, even
though we may have no direct evidence of the presence of a specific
pathogen. It is for this reason that we monitor the quality of our food and
water, and establish personal hygiene and public policies that attempt to
prevent contamination in the first place.
The fecal indicator bacteria are used to measure the sanitary quality of water
for recreational, industrial, agricultural and water supply purposes. The
fecal indicator bacteria, as noted above, are natural inhabitants of the
gastrointestinal tracts of humans and other warm-blooded animals. These
bacteria in general cause no harm. They are released into the environment
with feces, and are then exposed to a variety of environmental conditions that
eventually cause their death. In general, it is believed that the fecal
indicator cannot grow in natural environments, since they are adapted to
live in the gastrointestinal tract. Sunlight, temperature, competition with
bacteria found naturally in the water, predation by protozoa and other small
organisms, and toxic industrial wastes are all believed to influence the
survival of fecal indicator bacteria in the water. In addition, some wastes
are specifically treated to inhibit the survival of fecal bacteria and
pathogens. Studies have shown that fecal indicator bacteria survive from a
few hours up to several days in water, but may survive for days or months in
sediments, where they may be protected from sunlight and predators. The
survival time of fecal indicator bacteria in water is a function of many
environmental influences and there is no number that applies to all water
bodies, or even to all times of the year for a single body of water. We
assume that pathogens die at the same rate as fecal indicator bacteria.
Therefore, if we find relatively high numbers of fecal indicator bacteria in
the environment, we assume that there is an increased likelihood of
pathogens being present as well.
The fecal indicator bacteria are cultivated in the laboratory under conditions
which encourage their growth, prohibit the growth of non-fecal indicator
bacteria, and sometimes, provide special indications of their identity.
With current tests, a specific amount of water is passed through a filter,
which is then placed on a dish which contains the growth medium hardened
into a gel. The test dish (called a Petri dish or Petri plate) is incubated
for a specified amount of time at a specified temperature. At the end of
the test, each single cell of a fecal indicator bacterium present in the
original water will have reproduced sufficiently to produce a visible "colony"
of bacteria. To improve the accuracy of the test results, dyes or special
compounds may be included in the test growth medium which will result in the
fecal indicator bacteria being a different color than any non-fecal
indicator bacteria which might grow under the same conditions. Several
different tests may be conducted for total coliform bacteria, fecal coliform
bacteria, Escherichia coli (E. coli for short), as well as fecal
streptococci and enterococci. The total coliform bacteria are defined as "all
organisms that produce colonies with a golden-green metallic sheen within
24+2 hours when incubated at 35.0+ 0.5 oC" on a
specified growth medium. Fecal coliforms are a subgroup of total coliforms,
and Escherichia coli is a particular genus and species of fecal coliform. The
enterococci are a subgroup of the fecal streptococci. Slightly different
interpretations of water quality may occur based on the test performed. For
example, the fecal streptococci are believed to survive longer in water than
some coliform bacteria, and may be more associated with animal wastes than
with human wastes.
Current guidelines established by the U.S. Environmental Protection Agency
(USEPA) result from studies conducted at marine and freshwater beaches in
the late 1970's and early 1980's. In 1986, the USEPA recommended that E. coli
be used as an indicator of fecal contamination in recreational waters. The
standard was set at a geometric mean concentration of 126 colonies per 100
milliliters (mL) of water, which was estimated to be correlated with a
gastrointestinal illness rate of about 8 individuals per 1,000 swimmers.
How was this determined? Swimmers and non-swimmers were interviewed at
freshwater bathing beaches on Lake Erie in Pennsylvania and on Keystone Lake
near Tulsa, Oklahoma. Swimming was strictly defined as activity which
resulted in all upper body openings being exposed to the water. The beaches
had different levels of fecal indicator bacteria. After 8 to 10 days, the
swimmers and non-swimmers were interviewed again with regard to symptoms of
gastrointestinal or respiratory illness. The prevalence of gastrointestinal or
respiratory illness was then compared to the concentrations of E. coli,
enterococci and fecal coliforms on the day of swimming, as well as between
swimmers and non-swimmers. The conclusion of this study was that E.coli and
enterococci showed the strongest relationship with swimming-associated
gastrointestinal illness, but fecal coliform densities showed little or no
relation to gastrointestinal illness in swimmers. This study serves as a
reminder that it is not a simple task to arrive at recreational water
quality standards. No single test is infallible or correct for every
situation. Individuals use recreational waters in different ways, and are not
equally susceptible to disease due to their different behaviors and their
prior health conditions. Not every swimmer in these studies suffered
gastrointestinal illness.
There are many kinds of pathogens that might be transmitted in water. These
include bacteria, viruses and protozoa. Each type of bacterium, virus or
protozoan requires a different test. Many of these tests are expensive
because they require special materials or equipment or are time-consuming.
It is impractical to monitor water quality for every pathogen on a routine
basis.
The sources of fecal indicator bacteria include waste waters from sewage
treatment plants; other types of sewage inputs such as combined sewer outfalls
and drainage from septic tanks; runoff from agricultural fields or feedlots;
effluents from food processing plants (especially meats and beverages); and
stormwater runoff (which carries animal and bird droppings). The likelihood
that fecal indicator bacteria added to the environment by these means will
survive to be counted at a given water quality monitoring site is a function
of the distance of the site from such sources, and also a function of the
effect of all the environmental factors that influence bacterial survival.
An early study (Burm, R.J. and R.D. Vaughan, 1966, Journal of the Water
Pollution Control Federation, Vol. 38, pp. 400-409) compared the
bacteriological quality of the separate stormwater distribution of the city of
Ann Arbor, MI with that of the combined sewer system (specifically Conner
Creek drain) of Detroit. Samples were taken over several months. In April,
fecal coliform counts were 10,000 per 100 mL in the separate system (Ann
Arbor) but 890,000 per 100 mL for the Detroit combined system. By comparison,
in August, counts were 350,000 fecal coliforms per 100 mL at the Ann Arbor
site, and 4,400,000 per 100 mL at the Detroit site. Fecal streptococci
numbers were more similar between the two sites.
The U. S. Geological Survey has conducted several recent studies of fecal
indicator bacteria in recreational waters in Ohio, in cooperation with a
variety of Ohio State agencies including the City of Columbus Division of
Sewerage and Drainage, the City of Akron Public Utilities Bureau, the Summit
County Department of Environmental Services, the Ohio Water Development
Authority, the Ohio River Valley Water Sanitation Commission, the Northeast
Ohio Regional Sewer District and the Cuyahoga River Community Planning
Organization. These studies have provided data on fecal indicator bacteria
concentrations in selected rivers with respect to concentration,
relationship to recreational water-quality standards, and influence of
environmental factors such as rainfall, runoff, and wastewater chlorination
and dechlorination practices. These studies have determined that fecal
indicator concentrations may be highly variable along urban rivers (for
example, fecal coliform counts ranged from 20 colonies per 100 mL to 2,000,000
colonies per 100 mL for different sites and sampling dates on the Scioto River
in Columbus Ohio), and may exceed recreational water quality criteria even
in the absence of significant rainfall. In Ohio rivers, fecal coliform
densities and densities of E. coli were highly correlated. Current studies
involve the suspension of test bacteria in enclosed but permeable chambers
at various sites to determine the influence of treatment practices and
environmental factors on their survival. These studies should provide more
information on why fecal indicator counts are so variable, and what factors
influence this variability.
The U. S. Geological Survey has also collected and published water quality
data for the Clinton River at Mt. Clemens since 1975. Both fecal coliform and
fecal streptococci numbers were determined on a monthly or quarterly basis,
along with data on the chemical quality of the water. As with the Ohio
studies, densities varied greatly from one sampling time to another. These
data are currently being analyzed to determine if any water chemistry
variables may help to explain the bacterial densities.
The USEPA issued revised Primary Drinking Water Standards in mid-1994.
These standards address the source water quality, and vary somewhat with the
treatment technique used for preparation of the drinking water from the source
water. The Primary Standards suggest a presence/absence test for total
coliforms. If this test is used, and the sampling agency tests more than 40
samples, no more than 5% of those samples may test positive for total
coliforms. If fewer than 40 samples are used, no more than 1 sample may
test positive. In addition, maximum contaminant levels, which vary with
treatment technique, are specified for Giardia lamblia, Legionella (the
bacterium which causes Legionnaire's disease) and viruses. The USEPA Safe
Drinking Water Hotline provides more information. That number is 1-800-426-
4791.
USGS Contact:
Sheridan Haack- Project Coordinator
US Geological Survey
6520 Mercantile Way, Suite 5
Lansing, MI, 48911
Phone: 517-887-8909
E-Mail: SKHAACK@USGS.GOV
U.S. Department of the Interior,
U.S. Geological Survey
Water Resources Division,
Michigan District
Maintainer: Webmaster (gs-w-milns_webmaster@usgs.gov)
Last Modified: Wednesday, 04-Jan-2017 10:04:33 EST
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