Total coliform and E. coli bacteria test

Coliform are commonly found in the intestines of warm blooded animals and humans and are found in bodily waste, animal droppings, and naturally in soil. The total coliform group includes fecal coliform bacteria such as Escherichia coli (E .coli), as well as other types of coliform bacteria. Most of the fecal coliform in fecal material (feces) is comprised of E. coli. A strain of E. coli, serotype E. coli 0157:H7 is known to cause serious human illness.

Why test for total coliform bacteria?

Although the tests for coliform bacteria do not indicate their source, the presence of coliform organisms in water or surface samples indicates a possible contamination by sewage or animal wastes. Since sewage and animal wastes contain many disease causing organisms in addition to coliforms, disease causing organisms may be present whenever coliforms are found in drinking water. It's important to note that presence of total coliform does not necessarily indicate recent water contamination by fecal waste.

The presence of fecal coliform in well water may indicate recent contamination of the groundwater by human sewage or animal droppings which could contain other disease causing organisms. This is why coliform bacteria are considered “indicator organisms”. An indicator organism by itself is considered to cause no diseases in man or animals. Presence of indicator organisms in water, however, warns of the potential presence of disease causing organisms. By measuring the number of total coliform present in a sample a decision can be made as to the water's suitability for a given purpose.

However, there are problems with using the total coliform group as an indicator and this has resulted in an analyses for only those bacteria of the coliform group that are of fecal origin.

Sampling for total coliform bacteria

Procedure for sampling water from faucets, spigots, hydrants, or pumps for total coliform bacteria testing

1. Allow water to run from a faucet, spigot, hydrant or pump at a moderate rate (without splashing) for two to three minutes before sampling.
2. Carefully open sample containers just prior to collection and close immediately following collection. Do not lay the lid or cap down. Avoid touching the mouths and insides of the containers. Do not rinse the containers.
3. Properly label each sample container
4. Send samples to the lab immediately analyze samples as soon as possible after collection.

Procedure for sampling water from rivers, lakes and reservoirs for total coliform bacteria testing

When sampling a river, lake or reservoir, fill the sample container below the water surface. Do not sample near the edge or bank. Remove the cap, grasp the sample container near the bottom and plunge the container, mouth down, into the water. (This technique excludes any surface scum.) Fill the container by positioning the mouth into the current or, in nonflowing water, by tilting the bottle slightly and allowing it to fill slowly. Do not rinse. Label each sample container and analyze samples as soon as possible after collection.

Procedure for sampling sewage contaminated surfaces for total coliform bacteria testing

Swabs can be used on flat or irregular surfaces, such as corners or walls. When swabbing, target areas that were most likely to be contaminated with sewage. The recommended size of area to be sampled is approximately 100cm square. Best areas to swab are those areas that are not completely dry. If sampling dry areas, wet the swab before swabbing.

1. Aseptically, open the transport tube containing the swab. With sterilized gloved hands, remove the swab from the tube. Make sure the swab is moistened with the transport media. Replace the tube cap while collecting the sample to preserve the sterility of the tube.
2. Swab an area of approximately 100cm square (you can use a template to mark the area). Swab five times in a bottom to top direction and five times in a left to right direction. Put the swab back into the transport tube with the cotton in the media.
3. Label all samples with the sample identification, date and time of collection.
4. Send samples to the lab for analyses immediately after collection.

Total coliform bacteria testing

Total coliform bacteria testing is often performed via a colorimetric test. A colorimetric test is a test which involves a color change. A distinctive color change indicates the presence of total coliform bacteria. If a sample tests positive for coliform bacteria, a microbiologist will then perform further tests to determine if there is E. coli present.

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