Micrology Labs: Coliscan: E. coli and other coliform bacteria by Coliscan MF
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Official Method Name
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Coliscan MF |
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Current Revision
| 1999 |
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Media
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WATER |
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Instrumentation
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Membrane Filtration |
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Method Subcategory
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Microbiological |
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Method Source
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Citation
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Brief Method Summary
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100 mL water sample is filtered through a 0.45 micron membrane filter. Medium (1.75 - 2 ml) is dispensed onto a sterile pad in a 50 mm petri pad, or plates may be prepared by dispensing 5 mL of agar-based medium per 50 mm plate. The filter is then transferred to the plate, covered and incubated at 35C for 24 h. The presence of pink colonies is indicative of coliforms; the presence of blue/purple colonies is indicative of E. coli. Requirements: a low power (10-15 magnification) binocular wide-field dissecting microscope or equivalent may be necessary to to provide optimal viewing of the colonies. |
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Scope and Application
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ambient monitoring: all water - surface water, ground water, waste effluents, swimming pool, drinking water |
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Applicable Concentration Range
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20 - 80 CFU/100 mL is considered ideal for enumeration. Maximum: 200 CFU/100 mL; dilution is required for samples that exceed this level. |
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Interferences
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Waters containing sediment or suspended materials such as iron and manganese can clog the filter pores and prevent filtration, or mask target colonies and prevent accurate counting. Aeromonas may yield a positive coliform reaction under certain conditions, such as if one of the inhibitors in the medium is eliminated through adverse storage or outdating. Aeromonas does not interfere with E. coli determination. Sources of interference in MF methods (USEPA Fed Reg Aug. 2001): high turbidity, toxic compounds, or large numbers of non-coliform (background) bacteria, and organisms damaged by chlorine or toxic compounds. |
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Quality Control Requirements
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(Standard Methods, 20th ed., Section 9020 B8 and B9). Testing should be conducted on every lot of reagent with a known positive and negative strain. Verify filters are free of coliform bacteria. |
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Sample Handling
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Chill samples, 1oC to 4oC. Techniques for collection: Standard Methods for the Examination of Water and Wastewater, 20th Edition. L. Clesceri, A. Greenberg, and A. Eaton (editors). APHA: Washington, DC. 1998. Section 9060A Sample processing time: greater than 10 minutes. To minimize interferences causing underestimation of organism density in MF methods (USEPA Fed Reg Aug. 2001): replicates of smaller sample dilutions/volumes may be filtered and the results combined. |
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Maximum Holding Time
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Sample should be analyzed within 6 h after sampling and within 2 h from receipt of sample in lab for compliance or 24 h for routine monitoring (Standard Methods, 20th ed., Section 9060B); however, a 6 h holding time for all samples is highly recommended (Myers and Sylvester, 1997). Freeze kits for |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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