Fecal Contamination of Waters
. h t t p : / / W W W . S C I E N C E - P R O J E C T S . C O M / . . . . . . .

A Concerned Citizen's Kit:
Testing for Fecal Contamination of Surface Waters


.....One of the great advances in the history of public health has been the recognition that a community's fecal matter carries all the diseases in that population. If it's not properly treated even one sick person's wastes can spread the disease epidemically. Even before the "germ theory" was discovered by Pasteur and his associates, the virulence of untreated sewage was being recognized. London's cholera epidemics were often centered upon just one or two public wells that were found to be contaminated by sewage leaking into them.

..... While our current local health departments are charged with monitoring fecal pollution, restricted budgets limit the number of personnel available to do the job. But remember that this nation is built upon the notion of citizen participation. While many tasks require too much expertise for average concerned citizens to take matters into their own hands, there are yet many tasks that citizens can still do. This case of checking for fecal contamination is one. We are helped in this endeavor because some very clever scientists in the past have produced nearly fool-proof methods that are so simple that almost anyone who can fight through the thickets and mud that border streams can make a reasonably reliable test of waters for fecal contamination.

..... Before we get to the simple method, there are several facts that must be understood so that if positive results are found they may be interpretted knowledgeably.

  1. Most bacteria are good! All of us have huge numbers of dozens of different kinds of bacteria in our large intestines. .. Most of us are not sick from these and therefore those bacteria are usually not harmful to us. .. In fact, we could not live without them. .. Thus they are "good" bacteria, which help us in many ways - for example: digestion and keeping the few "bad" bacteria out.
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  2. "Indicator Bacteria." In order to test for fecal contamination, a common type of bacterium that is found essentially only in feces must be identified by a reasonably simple procedure. ..Thus if large numbers of that type of bacterium is found in surface waters, it is logical to assume that the water has become fecally contaminated since those bacteria don't come from anywhere else. The type of bacterium commonly used as this "indicator" is E. coli.
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  3. Shortly after 1900, a quick test for E. coli was found. It should be noted that most of the 47,000 known strains of this bacterium are "good" and only about 20 have any pathogenic attributes. .. Those twenty have given a bad rap to all the others, many of which we probably must have in us to survive. .. It's like saying all humans must be shunned because a few of us are bank robbers.
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    1. The quick test is seeing red colonies develop on MacConkey Agar petri plates. ..Very few other bacteria can make red ones when the plates are incubated (stored) overnight at room temperature. .. NO other bacteria can make red colonies if they have grown at 43.5C (110F).
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    2. While the E...coli itself is not necessarily dangerous in the water, the mere fact that fecal contamination is present is a strong danger signal because a few people in a large population will produce feces containing hepatitis, typhoid, HIV and other disease organisms. ..Why don't we just test for those? .. Because we have no simple and rapid tests, and because they would mostly likely be found in very low "needle-in-a-hay-stack" concentrations relative to E...coli. .. But to ingest only one dysentery bacterium would be sufficient to make most people extremely sick.
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    3. Most strains of E...coli will grow to make the red colonies on MacConkey Agar plates, but there are a few which don't. .. You might miss those few. BUT any red colony on a 43.5C plate will mean E...coli was in the water. .. Thus you will not get any false positives, but you might have some false negatives.
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    4. HOWEVER, news is beginning to filter in from the Virgin Islands, Oahu (Hawaii), Coronado Island (San Diego) and other subtropical sources that E...coli might not live exclusively in intestines. .. These localities are beginning to find that E...coli is a "soil bacterium" - meaning that they are growing in the soil along with zillions of other bacteria and fungi. Thus whenever it rains, some E...coli will wash into the streams and lagoons. ..There is growing uncertainty in these regions by sanitation inspectors that E...coli's presence is a reliable indicator of fecal contamination. .. A new fecal indicator bacterial type is being sought - one that is found nowhere else in nature. ..So if you are in the southern sections of the USA, raise your red flags slowly and tentatively if E...coli is found in your local stream, marsh or swamp. You may
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    5. Marine environments are not well tolerated by E...coli, and hence its use for monitoring fecal contamination of marine waters is a good positive if red colonies are found, but false negatives abound.


The Method

  1. Buy a box of sterile cotton swabs from your local drug store, and by a felt-tipped marking pen somewhere also.
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  2. Make or obtain from your local community hospital bacteriology technician several MacConkey Agar plates. .. Once you have them in hand, tape them shut with two or three strips joining the tops and bottoms of each of the plates, put them in a paper bag to keep them free of dusty breezes during transport. You will need one or two plates per sampling site. .. (Do not tape all the way around the plates, and do not use plastic bags for storage or transport as both will cause condensation buildup within the plates. .. Droplets of condensation will cause all the bacteria to run together.)
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  3. Go to your sampling site. .. Label one or two plates with that site's indentifying name. .. Loosen the tape.
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  4. Dip the cotton end of the swab into the water at the suspect site,
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  5. Open up one plate and paint the complete surface of that plate thoroughly with moist cotton tip. .. (You are being a bacteriologist and not a farmer - do not use the tip to plow the agar!)
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  6. If you have the luxury of having many plates, make a duplicate for each site.
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  7. Immediately take the plates to some room with no breezes.
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  8. If the agar surfaces are not damp, go to step 9. .. Otherwise, take off the tops from the bottoms and place them openings downwards so that one lip rests on a pencil. .. Allow the plates to remain in that position for about one hour so that excess moisture will evaporate. .. Once there are no longer any puddles on the agar surfaces...
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  9. Put the covers onto their respective bottoms and place them upside down in the place where you wish to incubate them. ..If you are so fortunate to have access to a 43.5C incubator, USE IT!
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  10. Allow the bacteria about 48 hrs to grow on the plates. .. (You may peek at 24 hrs!) .. Do you see any red colonies?
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  11. DO NOT KEEP the plates for days and days. .. They will soon overgrow with fuzzy fungi (molds) that are disgusting. .. So as soon as you see a large number of bacterial colonies on the surfaces of the agar, note whether there are any red colonies. .. AND then discard the plates this way: ..take some household bleach and dilute it to about 1 tablespoon per cup of water, and then flood the surfaces of the agar plates with that and allow to stand for about an hour to kill all the bacteria on the plates... Then pour off the liquid and put the plates in a zip-lock bag upon which you have written the word "decontaminated", and put it in the trash. ..Just in case, anyone at the landfill sees the petri plates they will see the note and know there is no danger.


IF YOU OBTAINED RED COLONIES - T H E N...

You should notify your local health department.

You might ask the laboratory people at your local sewage treatment facility to corroborate your test. ..They run sophisticated tests for E...coli every few hours, and could easily put your samples in line with their samples. ..Then you would have an official corroboration.

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