ISO 16649-3:2015
Microbiology of the food chain — Horizontal method for the enumeration of beta-glucuronidase-positive Escherichia coli — Part 3: Detection and most probable number technique using 5-bromo-4-chloro-3-indolyl-ß-D-glucuronide
ISO 16649-3:2015 specifies a horizontal method for the detection and enumeration of β-glucuronidase positive Escherichia coli, by means of the liquid-medium culture technique and calculation of the most probable number (MPN) after incubation at (37 ± 1) °C, then at (44 ± 1) °C. This part of ISO 16649 is applicable to the following:
- products intended for human consumption and the feeding of animals;
- environmental samples in the area of food production and food handling.
The method is suitable for the enumeration of cells of E. coli that might have been subjected to stress arising from dehydration, freezing, and exposure to a saline (such as marine) environment or damage by disinfectants such as chlorine-containing products.
A limitation of the applicability of this part of ISO 16649 is imposed by the susceptibility of the method to a large degree of variability. The method is intended to be applied and the results interpreted in the light of the information given in Clause 11.
This method has not been fully evaluated for all matrices (e.g. for milk and milk products). ISO 7251 is intended to be used for milk and milk products.
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Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
4.1 Detection method
4.2 Enumeration method
4.2.1 Inoculation of three or five tubes of double strength liquid selective enrichment medium [5.3.1.1 a)] with an equal volume of the test sample if the initial product is liquid, or with an equal volume of the initial suspension in the case of other pr
5 Dilution fluids and culture media
5.1 General
5.2 Dilution fluids
5.3 Culture media
5.3.1 Minerals modified glutamate medium (selective enrichment medium)
5.3.2 Tryptone bile glucoronide agar (second selective enrichment medium)
5.3.3 Performance testing for the quality assurance of the culture media
6 Apparatus and glassware
7 Sampling
8 Preparation of test sample
9 Procedure
9.1 Detection method
9.1.1 Test portion, initial suspension, and dilutions
9.1.2 Incubation of selective enrichment medium
9.1.3 Subculturing
9.1.4 Secondary incubation
9.1.5 Examination of the plates
9.1.6 Interpretation
9.2 Enumeration method
9.2.1 Test portion, initial suspension, and dilutions
9.2.2 Inoculation of the selective enrichment medium
9.2.3 Incubation
9.2.4 Subculturing
9.2.5 Second incubation
9.2.6 Examination of the plates
9.2.7 Interpretation
10 Expression of results
10.1 Detection method
10.2 Enumeration method
11 Precision
12 Test report
Bibliography
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Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
4.1 Detection method
4.2 Enumeration method
4.2.1 Inoculation of three or five tubes of double strength liquid selective enrichment medium [5.3.1.1 a)] with an equal volume of the test sample if the initial product is liquid, or with an equal volume of the initial suspension in the case of other pr
5 Dilution fluids and culture media
5.1 General
5.2 Dilution fluids
5.3 Culture media
5.3.1 Minerals modified glutamate medium (selective enrichment medium)
5.3.2 Tryptone bile glucoronide agar (second selective enrichment medium)
5.3.3 Performance testing for the quality assurance of the culture media
6 Apparatus and glassware
7 Sampling
8 Preparation of test sample
9 Procedure
9.1 Detection method
9.1.1 Test portion, initial suspension, and dilutions
9.1.2 Incubation of selective enrichment medium
9.1.3 Subculturing
9.1.4 Secondary incubation
9.1.5 Examination of the plates
9.1.6 Interpretation
9.2 Enumeration method
9.2.1 Test portion, initial suspension, and dilutions
9.2.2 Inoculation of the selective enrichment medium
9.2.3 Incubation
9.2.4 Subculturing
9.2.5 Second incubation
9.2.6 Examination of the plates
9.2.7 Interpretation
10 Expression of results
10.1 Detection method
10.2 Enumeration method
11 Precision
12 Test report
Bibliography