Environmental Services Program

Escherichia coli Analysis

Water Quality Monitoring Section staff use the IDEXX Colilert® and Quanti-Tray® system for detection and enumeration of Escherichia coli (E. coli) and total coliforms. The method can be applied to ambient Escherichia coli analysis being performedfresh waters, drinking waters and wastewaters.  The Colilert® method is not intended for use with marine waters.

The EPA-approved Colilert® method is based on Defined Substrate Technology®. The product utilizes nutrient indicators that produce color and/or fluoresce when metabolized by total coliforms and E. coli. After the reagent is added to the sample and incubated, it can detect these bacteria at 1 MPN (most probable number) per 100mL within 24 hours with as many as 2 million heterotrophic bacteria per 100mL present.