E. coli (Escherichia Coli) is a bacteria species that lives in the intestines of warm blooded animals. It is an indicator organism whose existence in a water body is evidence for fecal contamination and for the presence of microorganisms (excluding protozoans & viruses) that cause gastrointestinal diseases. E. coli in and of itself is not typically disease-causing.
According to the U.S. EPA National Primary Drinking Water Regulations safe drinking water should contain zero e. coli.
Vacuum Filter with pad
Syringe with hose
47mm Membrane Filters
50mm Petri Dishes with pads
Growth Medium with E. Coli stain
Where to Buy Materials:
- Micrology Laboratories – sells a complete kit (Coliscan MF Membrane Filter Kit – # CMFK2) for $60 that includes supplies for 20 tests, and sells refill kits (membrane filters, dishes, medium) as well as individual components. Note, this does not include the incubator, tweezers, or lighter. www.micrologylabs.com – under “Our Products” click “Membrane Filter”
- Millipore – sells e. coli growth medium with stain in 2mL plastic tubes (m-ColiBlue24® Broth). www.millipore.com – search “coliblue”
- Hach – sells an incubator (Hach Portable Incubator, 12 Vdc, 30 to 50 C (+/- 0.5 C) for $1000, a battery pack for $200, and an AC Adaptor or $60. This unit is designed to plug into a car cigarette lighter. www.hach.com – search “portable incubator”
1. Obtain a fresh water sample from the source to be tested.
2. Place a membrane filter (the white piece) onto the vacuum filter unit.
- Make sure there is a pad under the membrane filter.
- Use sterile tweezers for handling the membrane filter.
- Snap the plastic top down on top of the membrane filter.
3. Pour 100mL of sample water into the upper chamber of the vacuum filter.
4. Attach the syringe and slowly pull air out of the bottom chamber.
- If the syringe is fully pulled and the water stops flowing, just pull off the syringe, reset it, and start slowly pulling air out again.
- Make sure all water has been pulled through before you move on.
5. Place the membrane filter in a petri dish.
- Snap off the plastic upper chamber to get at the filter.
- Use sterile tweezers to move the filter.
- Leave the pad on the vacuum filter unit.
- Place the filter on top the pad in the petri dish.
- The petri dish has two halves, a smaller radius piece and a larger radius piece. Put the filter in the the half with the smaller radius.
6. Add 2mL of growth medium with e. coli stain into the petri dish.
- Spread it all the way around the plate.
- The medium will be absorbed into the pad.
- Use a 2mL pipet (one per test) to remove medium from a big bottle.
7. Incubate at 37 C for 24 hours.
- Plates should be placed upside down.
- Use an electric incubator if possible.
- If no electricity is present, place hot water bottles in an insulated container and change the water every 3 – 4 hours (or when the bottles become luke-warm).
- Three identical tests should be done for each water sample.
- Don’t forget to run a control group using clean water.
- Make sure to wash out the vacuum filter between tests.
9. Analyze – Count and record the number of e. coli colonies (their color will depend on the stain used).