The lab exercise assumes basic knowledge of prokaryotes (structure, function, metabolism, and respiration) and the functions and limitations of enzymes. Building upon this knowledge and using guided prompts, students brainstorm how to create an agar on which only coliform bacteria will grow and how to differentiate between Escherichia coli and other coliforms based on their enzymes. Finally, students filter surface water and place it on media that differentiates E. coli from other coliforms using an enzyme unique to E. coli. The resulting data are used to determine if the water meets the Minnesota state standards for safe swimming or drinking water.

Quantification of Escherichia Coli Contamination in Water (PDF)


Intended Audience








Learning Objectives

At the completion of this activity, each learner will be able to:

  1. utilize the unique enzymatic properties of bacteria to brainstorm a design for agar media that will allow for the quantification of E. coli and coliform bacteria.
  2. differentiate and enumerate colonies of E. coli and coliforms on agar media.
  3. interpret water quality standards for freshwater in terms of numbers of colonies of E. coli allowed per sample of water.


Student Background

Students should have a strong basic knowledge of prokaryotic cells, enzymes, and water quality before beginning this activity. These topics are also reviewed in the student handouts included with this activity.



Bacteria, E. coli, Coliform, Environmental sample, Lactose, Water quality, Enzyme, Petri dish, Filtration, Catalyst, Bioremediation


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