Coliform/E. coli results in 24 Hours
Simultaneously detects or quantifies both total coliforms and E. coli.
The IDEXX Colilert® Test is used around the world for the detection of coliforms and E. coli. With its patented Defined Substrate Technology® (DST®), Colilert is:
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Colilert: The standard for confident outcomes
Colilert® (20-test pack)
Colilert® (100-test pack)
Colilert® (200-test pack)
Pre-dispensed Colilert® (100-test pack)
Pre-dispensed Colilert® (200-test pack)
Snap packs and Quanti-Trays together.
How Colilert® works
Colilert uses the patented Defined Substrate Technology® (DST®) to simultaneously detect total coliforms and E. coli. Two nutrient-indicators, ONPG and MUG, are the major sources of carbon in Colilert and can be metabolised by the coliform enzyme β-galactosidase and the E. coli enzyme β-glucuronidase, respectively.
As coliforms grow in Colilert, they use β-galactosidase to metabolise ONPG and change it from colourless to yellow.
E. coli use β-glucuronidase to metabolise MUG and create fluorescence. Since most non-coliforms do not have these enzymes, they are unable to grow and interfere.
The few non-coliforms that do have these enzymes are selectively suppressed by Colilert's specifically formulated matrix.
This approach is different from traditional media, which provide a nutrient-rich environment that supports the growth of both target organisms and non-targets. When non-targets grow and mimic target organisms, false positives occur. Growth of non-targets can also suppress target organisms and give false negatives in traditional media. To suppress non-targets, traditional media often include high levels of salts, detergents or other selective agents that may inadvertently suppress target organisms and give further false negatives.
A step-by-step guide to using Colilert
Add reagent to sample and incubate at 35±0.5°C for 24 hours.
Add reagent to sample.
Seal in Quanti-Tray® Sealer and place in 35±0.5°C incubator for 24 hours (in other countries, the temperature requirement may be different per regulatory requirements).
Frequently asked questions and answers
Store at 2-30°C and away from light.
The Colilert comparator is a liquid color reference. Its purpose is to assist in distinguishing a minimal positive from a negative test result.
At 24-28 hours, compare each reaction vessel against the color comparator. Any yellow color or fluorescence equal to or greater than the comparator is considered positive.
The Colilert reagent powder should be dry, free flowing and white to off-white in colour. Any concerns about the colour of the powder or integrity of the powder should be directed to IDEXX Technical Service.
Yes, if they are negative. If an inoculated Colilert sample is inadvertently incubated over 28 hours, lack of yellow color is a valid negative test; a yellow color after the 28 hours is not valid and should be repeated or verified.
Yes, if they are positive. An inoculated Colilert sample that is positive for coliforms and E. coli before 24 hours is a valid positive test for both coliforms and E. coli. If the sample is positive before 24 hours for coliforms only, the sample is a valid positive test for coliforms. However, the sample should be incubated for a longer period (up to 24 hours, but not greater than 28 hours total time) to determine whether E. coli are present.
The reagent system was designed to suppress non-coliform ONPG or MUG positive bacteria for at least 28 hours. If incubation extends past 28 hours, it is possible that such bacteria will overcome the Colilert suppression system and react with ONPG or MUG. When incubation exceeds 28 hours, only negative results are valid. Positive results must be confirmed by classical methods.
Check with your local, state and/or federal authorities for proper disposal of bacteriological biohazard materials at your facility.
Yes. Colilert is U.S. Environmental Protection Agency (EPA)-approved as a method for total coliform and E. coli detection in drinking water and for E. coli detection in the following types of waters:
- Ambient waters (includes fresh, marine or estuarine surface water used for recreation, propagation of fish, shellfish, or wildlife; agriculture; industry; navigation; or as source water for drinking water facilities)
- Surface water
- Ground water