Coliscan media is a patented combination of color-producing chemicals and nutrients that detect coliforms and E. coli in specific colors for an easy identification and isolation. Meaning that a water sample may be added to the medium, and coliform bacteria will grow in either pink-magenta colonies or in purple-blue colonies, signifying E. coli. Generally other bacterial types will grow as non-colored colonies. There are two approaches to the Coliscan method, Coliscan Easygel and Coliscan MF.
When a sample size is of 1-5 mL, the Coliscan Easygel is ideal. An example of this would be the testing of river waters or other samples where there is normally a considerable amount of coliforms and E. coli. The sample can be added directly into the bottle of Coliscan Easygel, swirled, poured into a pretreated petri dish, incubated, and results can be read in 24-28 hours.
Normally, coliforms are found in soil and water and do not necessarily point towards the presence of fecal contamination, but Escherichia coli (E. coli) is a major bacterium in the human and animal intestinal tract and its presence in food or water indicates fecal contamination. The USEPA, United States Environmental Protection Agency, acknowledges that E. coli is the best sign of a health risk in fresh water and currently recommends testing for E. coli.
The other approach to testing for E. coli is using Coliscan MF, or a membrane filter. This is used with membrane filters, and it allows for much larger test samples of any filterable liquid. Coliscan MF is commonly used with potable water or treated wastewater that contains low levels of coliforms or E. coli. The steps to this approach include, the sample being filtered through a membrane filter, the bacteria become collected on the surface of the filter, it is then placed on a pad saturated with Coliscan MF liquid medium in a petri dish, where the colonies grow on the surface of the filter and are then they are counted.
If coliform colonies are present, a water insoluble pink pigment will be produced due to the enzyme galactosidase reacting with the colony and substrate. Therefore only deep blue-purple colonies are counted as E. coli.
Coliscan has numerous advantages over the other methods for water testing. It gives a simple, accurate and quantitative way to identify and differentiate coliforms and E. coli from other bacteria in water. It has a shelf life of 1 year and should be kept frozen until used.