Coliform Bacteria in Water: A Measure of Water Quality

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Coliform Bacteria in WaterA Measure of Water
Quality

• Sarah Palmer
• Tri-Valley ROP
• STEP/ETEC, LLNL

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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!

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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

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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?

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How can we test for Coliform Contamination?
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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

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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
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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.
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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.
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Classroom Application

• Development of a yellow color indicates the
  presence of coliform bacteria
• Clear is negative for coliform types

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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.

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E. coli has many sourcesReliable testing isan
important tool
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References

• IDEXX Laboratories (2003) Colilert.
  http//www.idexx.com/Water/Products/colilert/scien
  ce.cfm
• Gurpol Deol,M.Sc. (2003) Zone 7 Water Agency Del
  Valle Plant, personal communications