Coliform Bacteria in
Water:
A Measure of Water Quality
Sarah Palmer
Tri-Valley ROP
STEP/ETEC, LLNL
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?
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
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
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
A Defined Substrate Indicator
As coliforms grow in the defined substrate, they use ßgalactosidase to metabolize ONPG and change it from colorless
to yellow.
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.
Classroom Application
Development of
a yellow color
indicates the
presence of
coliform bacteria
Clear is negative
for coliform
types
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.
E. coli has many sources:
Reliable testing is
an important tool
References
IDEXX Laboratories (2003) Colilert™.
http://www.idexx.com/Water/Products/colil
ert/science.cfm
Gurpol Deol,M.Sc. (2003) Zone 7 Water
Agency Del Valle Plant, personal
communications