Micrology Labs: Easygel: E. coli and other coliform bacteria by Coliscan Easygel method

Summary
Analytes
Revision
Data and Sites

Official Method Name

Detection of waterborne coliforms and E. coli with Coliscan Easygel

Current Revision

1999

Media

WATER

Instrumentation

Gel Enumeration

Method Subcategory

Microbiological

Method Source

Micrology Labs

Citation

Detection of waterborne coliforms and E coli with Coliscan Easygel

Brief Method Summary

Preferred approach for all water samples (ideally 1 to 5 mL): a sample may be dispensed into the presterilized liquid medium and the mixture poured into a pretreated petri plate. Gelling occurs within 45 min. [Alternative approach: Presterilized liquid medium (13 mL/bottle for one plate) is poured into a pretreated (supplied with medium) petri plate and allowed to gel on a level surface. The solid surface may then be innoculated.] Gelled plates are incubated at a temperature of 35 C for 24 h. The presence of pink colonies is indicative of coliforms and blue/purple colonies is indicative of E. coli. Innoculum added to the liquid medium is limited to a maximum of 5 mL. Requirements: a low power (10 - 15 magnification) binocular wide-field dissecting microscope of equivalent may be necessary to provide optimal viewing of the colonies.

Scope and Application

ambient monitoring: all water: surface water, ground water, waste effluents

Applicable Concentration Range

20 - 80 CFU/100 mL is considered ideal for enumeration. Maximum: 200 CFU/100 mL; dilution is required for samples that exceed this level.

Interferences

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.

Quality Control Requirements

(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.

Sample Handling

Chill samples, 1^oC to 4^oC. 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.

Maximum Holding Time

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).

Relative Cost

Less than $50

Sample Preparation Methods

This method has 2 analytes associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
E. coli(68583-22-2) E. coli E.coli Escherichia coli	1.000 CFU/100 mL	N/A	N/A
Total coliforms(E761700) Total coliform Total coliforms	1.000 CFU/100 mL	N/A	N/A

Precision Descriptor Notes:	Aeromonas can yield false positives for coliform test 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. Deutsch, W. Comparative study of Coliscan Easygel and Standard Methods media in the enumeration and differentiation of E. coli and coliforms in river waters in Alabama. Unpublished study. Roth, J. N. Comparative studies of Coliscan Easygel and Standard Methods media for enumeration and differentiation of E. coli in coliforms in river water and treated wastewater effluents. General comments (USEPA Fed Reg Aug. 2001): Membrane filter (MF) methods are generally more precise in enumerating target organisms than MPN tests. Based on susceptibility to interferences, MF tests may underestimate the number of viable bacteria.
Detection Level Note:	Determined by using the largest volume, and the lowest number of organisms that can be counted. For example, if 5 mL was the largest volume, the detection would be 1 CFU/5 mL or 20 CFU/100 mL.

Precision Descriptor Notes:

Aeromonas can yield false positives for coliform test 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. Deutsch, W. Comparative study of Coliscan Easygel and Standard Methods media in the enumeration and differentiation of E. coli and coliforms in river waters in Alabama. Unpublished study. Roth, J. N. Comparative studies of Coliscan Easygel and Standard Methods media for enumeration and differentiation of E. coli in coliforms in river water and treated wastewater effluents. General comments (USEPA Fed Reg Aug. 2001): Membrane filter (MF) methods are generally more precise in enumerating target organisms than MPN tests. Based on susceptibility to interferences, MF tests may underestimate the number of viable bacteria.

Detection Level Note:

Determined by using the largest volume, and the lowest number of organisms that can be counted. For example, if 5 mL was the largest volume, the detection would be 1 CFU/5 mL or 20 CFU/100 mL.

Revision	PDF/Link
1999

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Micrology Labs: Easygel: E. coli and other coliform bacteria by Coliscan Easygel method

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