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Forms of micro-organisms in drinking water, part IV

Define Fecal coliform bacteria: Fecal coliform bacteria, such as Escherichia coli (E. coli), grow in the intestines of human beings and other warm-blooded animals. Since they are discarged in astronomical numbers (approximately 400 billion per day in the warm weather) in human excrement, their pres­ence in a water sample is an indication of human sewage.

Actually the total number of coliform bacteria that may enter a source of drinking water is reduced by several factors:

  • they die in large numbers because they cannot generally maintain themselves in sewage or in cleaner water;
  • they are removed in water purification processes;
  • they are destroyed in sewage treatment operations.

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Research has shown that the presence of fecal coliform bacteria indicates the entrance of human or animal wastes into water since coliform bacteria naturally exist in the intestines of humans and certain animals. Thus, the presence of these bacteria in water is accepted as proof that the water has been contaminated by human or animal wastes. Although such water may contain no pathogens, an infected person or animal, or a carrier of disease, could introduce pathogens at any moment, and immediate corrective action must be taken. The presence of fecal coliform bacteria shows water is contaminated by human wastes, and is potentially contaminated with pathogens. In short, these bacteria are a measure of guilt by association.

Conversely, the absence of coliform bacteria does not assure absence of pathogens, but their presence is considered unlikely. Just how can water be tested for the presence of coliform bacteria? These organisms cause the fermentation of lactose (the crystalline sugar compound in milk). When water containing coliform bacteria is placed in a lactose culture, it will cause fermentation resulting in the formation of gas. This confirms the suspicions. Or, coliform bacteria can be captured on a 0.45 micron membrane filter and grow into colonies large enough to see and count when incubated with a suitable agar growth medium or broth.

A recently developed coliform and E. coli analytical method makes use of the fact that coliform bacteria react with o-nitrophenyl-B-dgalactopyranoside (ONPG) to form a visible yellow color, and E. coli react with 4-methylum­belliferyl-B-d-glucuronide (MUG) to produce visible fluorescence under long wave ultraviolet light. By incorporating these chemicals along with growth broth in test tubes to be innoculated with the water sample, both total coliform and E. coli can be easily and accurately detected within 24 hours.

The EPA Primary Drinking Water Regulations indicate that water should contain an absence of coliform organisms or no more than one coliform-positive sample result when 5 to 39 samples are analyzed in a month, and no more than 5% coliform-positive sample results when 40 or more samples are analyzed each month.

Note: The standard of approximately one or 5% coliform-positive sample results is, of course, a standard of expediency. With even a single organism of this type in the water, there is always the possibility of infection, though extremely remote.

Recognizing the danger, what can be done to provide adequate protection against contamination? When a water supply becomes contaminated, correct the problem at once. This means going beyond treatment alone, important as this may be. It is a basic rule of water sanitation to get to the source of the problem and eliminate it. If a well, for example, becomes badly contaminated, it is necessary to trace the contamination to its source and, if possible, remedy the situation. It may even be necessary to seek out a new source of supply.

Note: Coliform bacteria were selected as a biological indicator of contamination or pollution because they satisfied the following requirements:

  • An organism serving as a reliable measure of contamination must indicate the potential presence of specific contaminating organisms in either a natural water or one subjected to treatment. Such an organism must react exactly as do the contaminating organisms both in the natural water supply and in a treated water.
  • The indicator organism must be present in greater number than is the contaminating organism. Unless this is true, the contaminating organism itself would serve the same purpose more directly.
  • The indicator organism must be readily identifiable by means of relatively simple analytical tests.
  • It is also important to evaluate the quantity of indicator organisms in the water since the degree of contamination is also an important factor.


Treatment of a water supply is a safety factor, not a corrective measure. Keep this in mind in the discussion that now follows.

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