Coliform Bacteria in Water ( Sarah PALMER )

Coliform Bacteria in Water:

A Measure of Water Quality

Sarah Palmer

Tri-Valley ROP


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!

Why Test?

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

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?

How can we test for Coliform Contamination?

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

Use of Lactose Broth

A Defined Substrate Indicator

A More Specific Indicator

Classroom Application

Development of a yellow color indicates the presence of coliform bacteria

Clear is negative for coliform types


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.

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


IDEXX Laboratories (2003) Colilert™.

Gurpol Deol,M.Sc. (2003) Zone 7 Water Agency Del Valle Plant,  personal communications

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