1. Coliform Bacteria in Water: A Measure of Water Quality
Sarah Palmer
Tri-Valley ROP
STEP/ETEC, LLNL

2. Significance of Coliforms
Coliform bacteria are a common and widely spread group of bacteria
Eschierichia coli is a species found in the lower gastrointestinal tract of many vertebrates and is indicative of FECAL CONTAMINATION!

3. Why Test?
E. coli itself is not dangerous to most healthy individuals at low concentration, BUT may indicate the presence of far more serious pathogens (and who wants poop in the water?)
It is also relatively easy to test for
Easy to kill the test cultures once they are grown

4. Testing for Drinking Water Safety
In the following slide we have a 5 minute “mini-course” in bacteriology
Make note of the procedures
What are negative controls?
What are positive controls?

5. How can we test for Coliform Contamination?

6. Testing for Coliform in the classroom
Use of a Lactose Broth with pH indicator
Straightforward, easy to use
Some false positives
Use of a commercially available Defined Substrate Media (From IDEXX Laboratories, Colilert™)
More expensive
Easy to use
Few false positives

7. Use of Lactose Broth
Lactose broth supports the growth of E. coli. Bromocresol purple turns from purple to yellow as the medium is acidified due to bacterial growth and metabolism

8. A Defined Substrate Indicator
As coliforms grow in the defined substrate, they use ß-galactosidase to metabolize ONPG and change it from colorless to yellow.

9. A More Specific Indicator
E. coli use ß-glucuronidase to metabolize MUG and create fluorescence. Since most non-coliforms do not have these enzymes, they are unable to grow and interfere.

10. Classroom Application
Development of a yellow color indicates the presence of coliform bacteria
Clear is negative for coliform types

11. Specificity
Tubes that turn yellow AND fluoresce under a UV lamp are positive for the E.coli form of the coliform group.
This indicates FECAL contamination.

12. E. coli has many sources: Reliable testing is an important tool

13. References
IDEXX Laboratories (2003) Colilert™.
Gurpol Deol,M.Sc. (2003) Zone 7 Water Agency Del Valle Plant, personal communications