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Test Methods
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Picture of bacteria plate with colonies growing on itDuring 2004 and 2005, volunteers in Indiana and Iowa were trained to assess E. coli using both field/home lab test methods and to collect samples that were analyzed in a state certified laboratory in Iowa. Six E. coli tests were assessed by these volunteer monitors. Following that sampling season, two test methods were recommended for use in all 6 participating states based on volunteer preference surveys, costs of the methods, and comparability of results between the methods and laboratory methods. In 2005 volunteers in MI, MN, OH, and WI initiated use of 3M Petrifilm and Coliscan Easgygel. Volunteers in all 6 participating states continue to test these two methods in 2006.

A brief description of each of the 6 test methods follows, with links to the distributors' websites and to the National Environmental Methods Index, so that users can find more detailed information about each method.

Coliscan Easygel (not incubated)

This test method, distributed by Micrology Laboratories, was assessed by volunteers in Indiana and Iowa. To use the kit for analysis, a small amount (0.5-5 mL) of water sample is poured into a bottle of Coliscan Easygel and mixed by swirling the bottle. The mixture is then poured into a labeled Petri dish/plate, covered, and swirled to uniformly distribute the sample. After sitting undisturbed for approximately 45 minutes, the Petri dishes are inverted. The dishes are then left at room temperature for 48 hours, at which time, purple/blue colonies (the E. coli colonies) on the plates are counted. E. coli numbers are represented in colony forming units (CFU) / 100 ml of water. For more information about this method visit the National Environmental Methods Index.

Coliscan Easygel (incubated)

This test method, distributed by Micrology Laboratories, is being assessed in all participating states. To use the kit for analysis, a small amount (0.5-5 mL) of water sample is poured into a bottle of Coliscan Easygel and mixed by swirling the bottle. Then, the mixture is poured into a labeled petri dish, covered, and swirled to uniformly distribute the sample. After sitting undisturbed for approximately 45 minutes, the Petri dishes are inverted and incubated at 35 degrees C for 48 hours. Then, like with the non-incubated Easygel method, purple/blue colonies (the E. coli colonies) on the plates are counted. E. coli numbers are represented in colony forming units (CFU) / 100 ml of water. For more information about this method visit the National Environmental Methods Index.

3M Petrifilm

This test method, distributed by 3M, is being assessed in all participating states. To use the kit for analysis, 1 mL of water sample is added to a Petrifilm petri plate. The petri plate is then incubated at 35 degrees C for 24 and 48 hours. Blue colonies are counted after both 24 and 48 hours to see how consistent the numbers are between incubation periods. E. coli numbers are represented in colony forming units (CFU) / 100 ml of water. This method is not included on the National Environmental Methods Index.

Coliscan MF Method

This test method was assessed only by volunteers in Indiana. Like the Easygel method, this method is distributed by Micrology Laboratories. To analyze for E. coli with this kit, a diluted sample of of water sample is poured through a filter. An agar-based medium is then added to a petri plate and the filter is placed on the plate. The petri plate is then covered and incubated at 35 degrees C for 24 hours. Blue/purple coloines are then counted and their presence indicates the presence of E. coli. E. coli numbers are represented in colony forming units (CFU) / 100 ml of water. For more information about this method visit the National Environmental Methods Index.

Colisure Method with the IDEXX Quanti-Tray/2000

IDEXX method photo showing Quanti-tray resultsThis test method is being assessed only by Iowa volunteers and is distributed by IDEXX Laboratories. To analyze for E. coli with this kit, a packet of reagent is added to 100 mL of sample water or a diluted sample and mixed by shaking. The mixed sample is then poured into a Quanti-Tray and sealed. The Quanti-Tray is then incubated at 35 degrees C and read at 24 and 48 hours. A UV light is used to determine the number of positive fecal coliform wells in the tray that also exhibit flourescence. A conversion table comes with the kit to determine the most probable number (MPN) of E. coli per 100 mL of water. For more information about this method visit the National Environmental Methods Index.

Colilert Method with the IDEXX Quanti-Tray/2000

This test kit is being assessed only by Iowa volunteers and is distributed by IDEXX Laboratories. To analyze for E. coli with this kit, a packet of reagent is added to 100 mL of sample water or a diluted sample and mixed by shaking. The mixed sample is then poured into a Quanti-Tray and sealed. The Quanti-Tray is then incubated at 35 degrees C and read after 24 hours. A UV light is used to determine the number of fecal coliform and E. coli colonies based on the number of wells in the tray that show yellow/flourescence. (The color change is different than with the Colisure Method.) A conversion table comes with the kit to determine the most probable number (MPN) of E. coli per 100 mL of water. For more information about this method visit the National Environmental Methods Index.

 

 

Updated August 5, 2008

 

 

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