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Coliform bacteria are found naturally in the environment but include all species of E. coli and other Gram-negative rod shaped bacteria found in the intestines of mammals, referred to as fecal coliforms. They are used to indicate whether fecal matter and possibly pathogenic organisms are present in water.
The enzyme substrate testing method involves the addition of nutrients and a chromogenic substrate to the sample followed by overnight incubation (Standard Method 9223). Coliforms utilize the substrate as a food source and produce a defined color change in the sample. If E. coli is present, the samples will fluoresce when illuminated with ultraviolet light. Using the IDEXX Quanti-Tray® system, the sample is divided into numerous wells within a tray so that the MPN of both coliform bacteria and E. coli bacteria can be determined.
Scientific Methods is certified by the Indiana State Health Department to detect total coliforms and E. coli by both the enzyme substrate method and the membrane filtration method.
The membrane filtration method using Coliscan (Micrology Labs) can be more precise than the enzyme substrate method in determining their concentrations. This method is very useful for treatment or validation studies.
The National Primary Drinking Water Regulation requires that there be zero coliforms present in both drinking water and groundwater. This regulation is enforced by the EPA and the standard is required by the Safe Drinking Water Act.
For beaches, E. coli levels should not exceed 88 cfu (colony forming units) per 100 mL in any one time sampling event or 47 cfu / 100 mL average of 3 samples over 60 days. Recreational waters not designated as beaches should not have over 406 E. coli cfu / 100 mL in any one time sampling event or 126 cfu / 100 mL average of 3 samples taken in a 60 day period.
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