These products add nutrient-indicators to a sample and rely on the presence of certain coliform enzymes in the sample. These enzymes will digest the nutrient indicators and fluoresce, giving a positive reading. 

The problem is that other bacteria in the environment can also produce enzymes that digest these nutrient-indicators, providing false positives. In addition, there are 36 species of Enterococcus, but only 8 of these are harmful to humans, again providing potentially false indicators when these non-harmful species are detected.

Sources of fecal contamination in these cases also remains ambiguous. Using eDNA means that we can detect multiple potential hosts as well as the fecal bacteria at the same time. 

There are quite a few papers out there calling products like Colilert and Enterolert into question on their effectiveness. 

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