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Colilert-18 - IDEXX Water

Principle: Uses proprietary Defined Substrate Technology (DST) nutrient indicators - ONPG and MUG

Automation: No

Approvals: U.S. EPA Approval; ISO 9308-2:2012

Suitability: Detction of both total coliforms and Escherichia coli in water

Capital equipment required: Yes


Colilert-18 is a liquid culture method that simultaneously detects both total coliforms and Escherichia coli in water, giving confirmed results in 18 hours.

Principle: The Colilert-18 test uses proprietary Defined Substrate Technology (DST) nutrient indicators ONPG and MUG to detect coliforms and E. coli. Coliforms use their β-galactosidase enzyme 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-18 test’s specifically formulated matrix.

Approvals: U.S. EPA Approval: Colilert-18/Quanti-Tray has US EPA Approval for detection of coliforms and E.coli in Drinking Water, Surface Water Ground Water and Waste Water.

ISO 9308-2:2012: Colilert-18 is the ISO 9308-2 standard for Water Quality - Enumeration of Escherichia coli and coliform bacteria - Part 2: Most probable number method.

Colilert-18, (ISO 9308-2) is a reference method in the European Drinking Water Directive 2015/1787

AFNOR NF Validation (IDX 33/01-11/09) - Colilert-18/Quanti-Tray is validated for the enumeration of β-glucuronidase positive Escherichia coli and β-galactosidase positive coliform bacteria in drinking waters for human consumption.

SCA Blue Book: Colilert-18 is specified in Microbiology of Drinking Water (MoDW) Part 4: Methods for the Isolation and enumeration of coliform bacteria and Escherichia coli (including E.coli O157 H7) (2016) - Colilert®-18 (Method D).

A more exhaustive list of approvals is available on request

Key Points:


  • Identifies E. coli specifically, avoiding unnecessary remedial action caused by non-target organisms.
  • Suppresses up to 2 million heterotrophs per 100 mL.
  • Eliminates the subjective interpretation found with traditional methods.
  • Detects a single viable coliform or E. coli per sample.


  • Under 1-minute hands-on sample preparation time.
  • Detects coliforms and E. coli simultaneously in 18 hours or less.
  • No confirmations needed.
  • No glassware cleaning or colony counting.


  • Ease of use simplifies training.
  • Unit-dosed packaging eliminates media preparation.
  • No repeat testing due to clogged filters or heterotrophic interference.
  • Quality Control (QC) procedure can be done in 15 minutes.

Operational Value

  • Faster results mean that you can act sooner to prevent the spread of contamination.
  • Extremely low false positives rates reduce the incidence of false alarms giving greater confidence to operations, reduced uncertainty and unnecessary expense.


  • Minimises evening and weekend work.
  • Up to 15-month shelf life at room temperature.


  • Can be used for presence/absence (P/A) or quantification testing with Quanti-Tray® and Quanti-Tray®/2000.



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Company contact details:

IDEXX Laboratories Inc view full details
United States

Website: Visit Website
Tel: +1 800 321 0207