Modified Colitag: ATP D05-0035: E. coli and other Total Coliforms in Water using Modified Colitag Medium
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Official Method Name
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Modified Colitag Test Method for the Simultaneous Detection of E. coli and other Total Coliforms in Water |
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Current Revision
| Version 2.0, June 2020 |
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Media
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WATER |
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Instrumentation
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Not Applicable |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Modified Colitag Test Method for the Simultaneous Detection of E. coli and other Total Coliforms in Water (ATP D05-0035): August 28, 2009 |
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Brief Method Summary
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Modified Colitag is a one-step, ready-to-use, dehydrated medium for analysis of water samples. For presence/absence testing, one packet of medium is mixed with a 100-mL sample of water and incubated at 35±0.5°C for 16 to 48 hours. If results are intended to be read before 22 hours incubation, samples must be pre-warmed for 7-10 minutes in a 44.5 ±0.2°C water bath. If yellow color is observed, coliforms are present. If blue fluorescence is observed under 365 nm ultraviolet (UV) light, E. coli are present. For enumeration of E. coli and other coliforms, Modified Colitag¿ is suitable in a variety of Most Probable Number (MPN) formats, which be looked up in Table 9221:III of Section 9221C Estimation of Bacterial Density in the Standard Methods for the Examination of Water and Wastewater. |
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Scope and Application
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Modified Colitag is a selective and differential medium for the simultaneous determination of the presence or absence or enumeration of E. coli and other total coliforms in water. Modified Colitag is for use in the Environmental Protection Agency's survey and monitoring programs under the Safe Drinking Water Act. This method is for use in accordance with the National Primary Drinking Water Regulations at 40 CFR Part 141.4. This method allows for the detection of coliform bacteria and/or E. coli from 16 - 48 hours and does not require further confirmation or verification steps. This method is US EPA approved for compliance monitoring of public water systems as required by the Total Coliform Rule. |
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Applicable Concentration Range
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Modified Colitag is capable of detecting 1 colony forming unit (CFU) of chlorine-injured E. coli or other coliform bacteria per 100-mL of water sample. There is no upper limit of detection in the MPN format as dilutions are used to detect and enumerate bacteria. |
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Interferences
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There are no known chemical interferences that would be found in drinking water or source water that would inhibit or interfere with the development of color or the production of fluorescence when one uses Modified Colitag medium. Heterotrophic bacteria greater than 104/ml can yield positive coliform reactions. |
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Quality Control Requirements
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Each lot of Modified Colitag should be tested for quality. Four presence/absence packs or single strength MPN tubes will be needed; the first as a blank (uninoculated), and the others to be inoculated with a representative positive and negative cultures. For additional guidance or clarity regarding QC, refer to Standard Methods, Sections 9223 B and 9020 A. |
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Sample Handling
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Water samples should be collected in sterile, plastic or glass leakproof containers and sufficient sodium thiosulfate to neutralize chlorine at the time of collection. Samples should be placed on ice or refrigerated at a temperature of 1-10oC during transit to the laboratory. |
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Maximum Holding Time
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Samples should be tested as soon as possible after collection. |
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Relative Cost
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Unknown |
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Sample Preparation Methods
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