Coliform Bacteria

Background Information

If coliform bacteria are present in the water supply it is an indication that the water supply may be contaminated with sewage or other decomposing waste. Usually coliform bacteria are found in greater abundance on the surface film of the water or in the sediments on the bottom. There are many types of coliform bacteria. Coliform bacteria naturally occur in the human digestive tract and aid in the digestion or breakdown of food.

Test Procedure

This test simply tests for the presence or absence of coliform bacteria; it does not give a quantitative result. The kit used for this test is the Kemtec Coliform Test Kit supplied by Nasco (or other supplier).

1. Collect the water sample to be tested in a clean vial.
2. Carefully remove the cap from a tube of lactose broth (purple vial).
3. Measure 1 mL of the water sample using a sterile pipette and add it to the tube of lactose broth.
4. Re-cap the tube of lactose broth and incubate the tube (20-32 C) in an upright position for 24-48 hours.
5. If the broth is still purple after 48 hours, coliform bacteria are not present. If the broth is green or yellow after 48 hours, then coliform bacteria are present.

Results for this test should indicate whether coliform bacteria are present or not (yes/no). However, if a more specific fecal coliform test is performed, please report your results as number of fecal coliform colonies per 100 ml sample of water.

What to Expect

An absence of any coliform bacteria in your water supply is a sign of a healthy river. The presence of coliform bacteria may be an indication of a polluted water supply but it would be necessary to do further tests in order to identify the specific bacteria present and the level of contamination. The coliform bacteria count should not exceed 0 colonies per 100 mL sample of water for drinking water supplies. The limits for swimming and boating/fishing are higher.

References