Detecting E. coli in Water: A Guide to the Membrane Filter Technique

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Detecting E. coli Using Membrane Filter Technique

In the laboratory, E. coli can be detected using the membrane filter technique, a common method for water quality analysis. Here's how it's done:

  1. Sample Collection: Collect a water sample from the source to be tested.

  2. Filtration: Pass the water sample through a membrane filter with a pore size small enough to trap bacteria. Typically, filters with a pore size of 0.45 micrometers are used.

  3. Incubation: Place the membrane filter on a nutrient agar medium specifically designed for E. coli growth. Incubate the agar plates at a suitable temperature (usually 35-37°C) for 24 hours.

  4. Colonies Observation: After incubation, examine the agar plates for the presence of characteristic E. coli colonies. E. coli colonies typically appear as small, pinkish-red colonies with a metallic sheen on Eosin Methylene Blue (EMB) agar.

  5. Confirmation: Perform additional biochemical tests (e.g., Indole test, Methyl Red test) to confirm the presence of E. coli in suspected colonies.

  6. Enumeration: Count the number of confirmed E. coli colonies on the agar plates to determine the concentration of E. coli in the water sample.

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