Colilert-18
Simultaneously detects both total coliforms and Escherichia coli in water, or fecal coliforms in wastewater, giving you results in 18 hours.
- Read afternoon samples the next morning—before the next day’s samples arrive.
- Lift boil water alerts in 18 hours.
- Provide results in record time for real estate, new well, and new construction samples.
- Read Friday samples early Saturday, leaving the rest of the weekend free.
The Science
The Colilert-18 test uses a proprietary Defined Substrate Technology (DST) nutrient indicators ONPG and MUG to detect coliforms and E. coli. Coliforms use their β-galactosidase enzyme to metabolize ONPG and change it from colorless to yellow.
E. coli use β-glucuronidase to metabolize 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 the Colilert-18 test’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 nontargets. When nontargets grow and mimic target organisms, false positives occur. Growth of nontargets can also suppress target organisms and give false negatives in traditional media. To suppress nontargets, traditional media often include high levels of salts, detergents, or other selective agents that may inadvertently suppress target organisms and give further false negatives.
Only IDEXX reagents have been validated and are approved for use with Quanti-Tray and Quanti-Tray/2000.
Presence/Absence
Step 1
Step 1
Step 1
Add reagent to sample and incubate at 35°C ± 0.5°C for 18 hours.
Step 2
Step 1
Step 1
Read results:
Colorless = negative
Yellow = total coliforms
Yellow/fluorescent = E. coli
Quantification
Step 1
Step 1
Step 1
Add reagent to sample.
Step 2
Step 1
Step 1
Pour into Quanti-Tray (counts from 1–200) or Quanti-Tray/2000 (counts from 1–2,419)
Step 3
Step 1
Step 4 - Quanti-Tray
Seal in Quanti-Tray Sealer and place in 35°C ± 0.5°C incubator for 18 hours (in other countries, the temperature requirement may be different per regulatory requirements).
Step 4 - Quanti-Tray
Step 4 - Quanti-Tray/2000
Step 4 - Quanti-Tray
Quanti-Tray—Read results:
- Yellow wells = total coliforms
- Yellow/fluorescent wells = E. coli
- Count positive wells and refer to MPN table
Step 4 - Quanti-Tray/2000
Step 4 - Quanti-Tray/2000
Step 4 - Quanti-Tray/2000
Quanti-Tray/2000—Read results:
- Yellow wells = total coliforms
- Yellow/fluorescent wells = E. coli
- Count positive wells and refer to MPN table