Scientific Basis: 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 metabolized by the coliform enzyme β-galactosidase
and the E. coli enzyme β-glucuronidase, respectively.
As coliforms grow in Colilert, they use β-galactosidase
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 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—which may
inadvertently suppress target organisms and give further false negatives.
All IDEXX DST reagents can be used in a presence/absence (P/A) vessel, Quanti-Tray®, or Quanti-Tray®/2000.
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