Colilert
The Colilert test simultaneously detects or quantifies both total coliforms and Escherichia coli, with results in 24 hours.
The Science
The Colilert Test uses proprietary 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 the Colilert Test, 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 the Colilert 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 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 24 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 24 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