Materials and Resources

MWRA Coliform handout

Note: This text is made available courtesy of the Massachusetts Water Resources Authority. We have scanned in the original manual pages and converted the files to text. Unfortunately, the pictures were lost and there are some irregularities in the formatting. Our apologies for the inconvenience.

TEST 8: TOTAL COLIFORM BACTERIA

Brief Summary

A simple presumptive test that indicates the presence of total coliform bacteria in a water sample. After 48 hours of incubation at room temperature, a lactose broth solution changes colors from purple to yellow if coliform is present.

Background

Coliform is a group of generally nonpathogenic bacteria that live throughout the environment. One type of coliform, fecal coliform, lives in the intestinal tract of warm blooded animals and helps digest foods. It is not harmful in and of itself, but it serves as an indicator of the presence of pathogenic bacteria. Fecal coliform bacteria are abundant in human feces, so they are easy to find whenever sewage is present. If you find coliform bacteria in water, you can be sure that other bacteria, viruses or parasites are also present. Some of these might cause diseases.

Testing for particular pathogens in water is usually difficult and time consuming. Coliform bacteria, however, are fairly easy to test for, and they usually occur with other pathogens.

That is why people who monitor water quality use this group as an indicator. In water with high total coliform counts, about 10% of the coliform will be fecal coliform.

This kit uses a simple presumptive test for the presence of total coliform bacteria. The test uses a lactose broth that changes color from purple to yellow in the presence of coliform bacteria. Since it is a presumptive test, it is impossible to calculate the quantity of coliform in the water but this test does not require special equipment or incubation.

WATER-BORNE DISEASES ARE STILL WORLDWIDE KILLERS

According to the World Health Organization, throughout the world, 4.3 million people, mostly children, die every year from diarrhea caused by water-borne bacteria! That is more than the population of Norway. Other water-borne diseases, such as typhoid, cause seven million deaths and seven billion illnesses each year. Proper water treatment and disinfection of sewage prevent large-scale epidemics.

Sources of Coliform

• Combined sewage systems carry both sanitary wastes - from toilets, washers and sinks - and storm runoff. During, rains, sewer pipes are too small to handle the combined flow, so part of it is diverted into a river, bay or harbor. This storm overflow contains untreated or inadequately treated sewage.

• Agricultural and rural runoff carries wastes from birds and animals. -

• Improperly working septic tanks and cesspools can allow untreated wastewater to seep into the groundwater.

Testing for Total Coliform Bacteria

Overview:	The conventional test for total coliform bacteria requires special equipment, precise lab procedures, incubation, and culture counting. This kit contains only a simple presumptive test for total coliform bacteria. It does not measure the type or quantity of coliform bacteria, only their presence. The coliform testing, tubes contain a purple-colored lactose broth that is sensitive to coliform bacteria. If coliform bacteria are present, the purple liquid will turn yellow within 48 hours when incubated at room temperature.
Length of Test:	2 minutes in the field; 48 hours incubation time.
Difficulty of Test:	Simple
Protective Clothing:	Rubber gloves
Expected Results:	Most natural water sources will contain some coliform bacteria, so expect a positive result. Tap water and bottled water should not contain any coliform bacteria. If a tap water sample tests positive, let the water run for a few minutes and test it again. If it continues to test positive, you may want to call the health department. If bottled water from a supermarket tests positive, retest it. If it continues to test positive, report it to a local health official. If bottled water from your water cooler tests positive, retest it. Your water cooler may need disinfecting and your water distributor can provide instructions. After cleaning the cooler, test the water again using another bottle of water.

PROCEDURE

1. The coliform tubes are capped and about one-half full of purple liquid. Before removing the cap, write the date, time, and source of the water sample on the tube itself. (Either use tape or a permanent marking pen.)

2. Remove the cap from one of the coliform testing tubes. Fill the tube with your water sample to about 1 cm from the top. (The tube has a small shoulder at that level.)

3. Replace the cap.

4. Leave the tube in a safe, warm place for 48 hours.

   NOTE: Cool temperatures will not change the results of the test; temperatures of less than 20 *C (68 *F), however, may slow down the color change if coliform is present.

5. After 48 hours, examine the tube and record the results on the Data Recording Form.

   Purple = No coliform bacteria present
   Yellow = Coliform bacteria in the water sample

6. Add several drops of chlorine bleach to the tube to kill the bacteria. Flush the contents of the tube down the drain and discard the tube. DO NOT dispose of the sample without first disinfecting it.

Interpreting Results

Positive results indicate the presence of total coliform bacteria from warm-blooded animals and various soil organisms. People should not drink that water! Total coliform counts are usually about 10 times higher than fecal coliform. Thus, if you find total coliform bacteria, your sample probably contains fecal coliform and other disease-carrying pathogens. You cannot tell whether fecal coliform bacteria came from human sewage or animal waste without performing other laboratory tests.

Extension Activities

1. Rinse your hands in clean water (water not contaminated with coliform), then test that wash water. Were you carrying coliform on your hands? The results might be a strong argument in favor of regular hand washing.

2. Disinfect a sample of coliform-contaminated water and test it again. You may disinfect it by boiling, the water sample or adding a drop of chlorine bleach. Try several different disinfection techniques and see if they all work equally well.

Back to:

• Materials and Resources