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1、Australian StandardiAS 5013.32009ISO 4831:2006AS 5013.32009Food microbiologyMethod 3: Microbiology of food and animal feeding stuffsHorizontal method for the detection and enumeration of coliforms Most probable number techniquePREFACEThis Standard was prepared by the Standards Australia Committee FT
2、-024, Food Products and Constituted Subcommittee FT-024-01, Food Microbiology, to supersede AS 5013.32004, Food microbiology, Method 3: MicrobiologyGeneral guidance for the enumeration of coliformsMost probable number technique.This Standard is identical with and reproduced from ISO 4831:2006, Micro
3、biology of food and animal feeding stuffsHorizontal method for the detection and enumeration of coliformsMost probable number technique.The objective of this Standard is to provide general guidance for the detection and the enumeration of coliforms present in products intended for human consumption
4、or feeding of animals, by means of calculation of the most probable number (MPN) after incubation at30C or 37C in a liquid medium, this temperature forming the subject of agreementbetween parties concerned.Clauses 4 (Principle), 9 (Procedure) and 10 (Expression of results) of AS 5013.32004 have been
5、 technically revised. The main changes are as follows:(a) The alternative procedure of incubation at 35C has been deleted.(b) Detection and enumeration of coliforms are covered (Clauses 4 and 9).(c) Description of the MPN and the CCT have been omitted (Clause 10) and reference is given to AS 5013.14
6、 (ISO 7218).As this Standard is reproduced from an international standard, the following applies:(i) Its number appears on the cover and title page while the international standard number appears only on the cover.(ii) In the source text this International Standard should read this Australian Standa
7、rd. (iii)A full point substitutes for a comma when referring to a decimal marker.(iv)Substitute mL for ml wherever it appears.References to International Standards should be replaced by references to AustralianStandards, as follows:www.standards.org.auiiiReference to International Standard Australia
8、 StandardISOAS6887Microbiology of food and animal5013Food microbiologyfeeding stuffsPreparation of test samples, initial suspension and decimal dilutions for microbiological examinations6887-1 Part 1: General rules for the preparation of the initial suspension and decimal dilutions6887-2 Part 2: Spe
9、cific rules for the preparation of meat and meat products6887-3 Part 3: Specific rules for the preparation of fish and fishery products6887-4 Part 4: Specific rules for the preparation of products other than milk and milk products, meat and meat products and fish and fishery products7218Microbiology
10、 of food and animal feeding stuffsGeneral requirements and guidance for microbiological examinations8261Milk and milk productsGeneral guidance for the preparation of test samples, initial suspensions and decimal dilutions for microbiological examination5013.11.1 Method 11.1: Microbiology of food and
11、 animal feeding stuffs Preparation of test samples initial suspension and decimal dilutions formicrobiological examinationGeneral rules for the preparation of the initial suspension and decimal dilutions5013.11.2 Method 11.2: Microbiology of food and animal feeding stuffs Preparation of test samples
12、 initial suspension and decimal dilutions for microbiological examination Specific rules for the preparation of meat and meat products5013.11.3 Method 11.3: Microbiology of food and animal feeding stuffs Preparation of test samples initial suspension and decimal dilutions for microbiological examina
13、tion Specific rules for the preparation of fish and fishery products5013.11.4 Method 11.4: Microbiology of food and animal feeding stuffs Preparation of test sample initial suspension and decimal dilutions for microbiological examination Specific rules for the preparation of products other than milk
14、 and milk products, meat and meat products and fish and fishery products5013.14Method 14: Microbiology of food and animal feeding stuffsGeneral rules for microbiological examinations5013.17Method 17: Milk and milk products General guidance for the preparationof test samples, initial suspensions and
15、decimal dilutions for microbiologicalexaminationOnly international references that have been adopted as Australian Standards have been listed.The Standard is downloaded from Standard SharingThe laboratory should have a clearly defined quality control system to ensure that the apparatus, culture med
16、ia, reagents and technique are suitable for the test. The use of positive controls is part of this system.The method given in this Standard is for use for all foods for the enumeration of coliforms.The term normative has been used in this Standard to define the application of the annex to which it a
17、pplies. A normative annex is an integral part of a Standard.vINTRODUCTIONBecause of the large variety of food and feed products, this horizontal method may not be appropriate in every detail for certain products. In this case, different methods, which are specific to these products, may be used if a
18、bsolutely necessary for justified technical reasons. Nevertheless, every attempt should be made to apply this horizontal method as far as possible.When this International Standard is next reviewed, account will be taken of all information then available regarding the extent to which this horizontal
19、method has been followed and the reasons for deviations from this method in the case of particular products.The harmonization of test methods cannot be immediate and, for certain groups of products, International Standards and/or national standards may already exist that do not comply with this hori
20、zontal method. It is hoped that when such standards are reviewed they will be changed to comply with this International Standard so that eventually the only remaining departures from this horizontal method will be those necessary for well-established technical reasons.The technique described in this
21、 International Standard is less precise than that described in ISO 4832 1, but allows a microbiological examination to be carried out on a larger test portion, thus permitting a lower number of coliforms per gram or per millilitre of product to be detected. Moreover, since the definition of “colifor
22、ms” adopted in the two documents is different, the microorganisms enumerated are not necessarily the same.For any particular product, the method to be chosen will be specified in the International Standard dealing with that product.The Standard is downloaded from Standard SharingFor the purposes of
23、 a practicable test method, the definition of “coliforms” given in Clause 3 and used as the basis for the procedure is not necessarily identical to corresponding definitions given in other published texts. A proportion of strains of the microorganisms described in other published texts as “coliforms
24、” (including Escherichia coli) fail to produce enough gas to be detectable by use of a Durham tube (i.e. “anaerogenic strains”). Therefore the method described in this International Standard will not detect all strains of the microorganisms referred to in other publications as “(presumptive) colifor
25、ms” (e.g. certain strains of Citrobacter, Enterobacter, Klebsiella) (see Reference 2).www.standards.org.au Standards Australia1ScopeThis International Standard gives general guidelines for the detection and the enumeration of coliforms. It is applicable toproducts intended for human consumption and
26、for the feeding of animals, andenvironmental samples in the area of food production and food handling.Enumeration is carried out by calculation of the most probable number (MPN) after incubation in a liquidmedium at 30 C or 37 C.NOTEThe temperature is subject to agreement between the parties concern
27、ed. In the case of milk and milk products, the temperature of incubation is 30 C.This enumeration method is applicable when the number sought is expected to be in the range 1 to 100 per millilitre or per gram of test sample.A limitation on the applicability of this International Standard is imposed
28、by the susceptibility of the method to a large degree of variability. The information given in Clause 11 provides guidance on the applicability of the method and on the interpretation of the results.2Normative referencesThe following referenced documents are indispensable for the application of this
29、 document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 6887 (all parts), Microbiology of food and animal feeding stuffs Preparation of test samples, initial suspension and decimal d
30、ilutions for microbiological examinationISO 7218, Microbiology of food and animal feeding stuffs General requirements and guidance for microbiological examinationsISO 8261, Milk and milk products General guidance for the preparation of test samples, initial suspensions and decimal dilutions for micr
31、obiological examinationISO/TS 11133-1, Microbiology of food and animal feeding stuffs Guidelines on preparation and production of culture media Part 1: General guidelines on quality assurance for the preparation of culture media in the laboratoryISO/TS 11133-2:2003, Microbiology of food and animal f
32、eeding stuffs Guidelines on preparation and production of culture media Part 2: Practical guidelines on performance testing of culture media13The Standard is downloaded from Standard Sharing3Terms and definitionsFor the purposes of this document, the following terms and definitions apply.3.1 colifo
33、rmsbacteria which, at the specified temperature (i.e. 30 C or 37 C, as agreed) cause fermentation of lactose with the production of gas under the test conditions specified in this International Standard3.2detection of coliformsdetermination of the presence or absence of these bacteria, in a particul
34、ar quantity of product, when tests are carried out in accordance with the method specified in this International Standard3.3enumeration of coliformsmost probable number of coliforms found per millilitre or per gram of the test sample, when the test is carried out in accordance with the method specif
35、ied in this International Standard4Principle4.1Detection of coliforms4.1.1A tube of selective enrichment broth is inoculated with the test portion and incubated at 30 C or 37 C (as agreed) for 24 h or 48 h.4.1.2A tube of confirmation medium is inoculated from the tube obtained in 4.1.1 when opacity
36、and/or gas formation has been noted, and incubated at 30 C or 37 C (as agreed) for 24 h or 48 h.4.1.3The presence of coliforms is confirmed in the case that opacity and gas formation have been noted after examination of the tube obtained in 4.1.2.4.2Enumeration by the MPN technique4.2.1Three tubes o
37、f double-strength liquid selective enrichment medium are inoculated with a specified quantity of the test sample if the initial product is liquid, or with a specified quantity of an initial suspension in the case of other products.4.2.2Three tubes of single-strength liquid selective enrichment mediu
38、m are inoculated with a specified quantity of the test sample if the initial product is liquid, or with a specified quantity of an initial suspension in the case of other products. Then, under the same conditions, further tubes of single-strength medium are inoculated with decimal dilutions of the t
39、est sample or of the initial suspension.4.2.3The tubes containing double-strength selective enrichment medium are incubated at 30 C or 37 C (as agreed) for 24 h, and the tubes containing single-strength medium are incubated for 24 h or 48 h, after which period these tubes are examined for gas format
40、ion or opacity preventing the detection of gas formation.4.2.4A series of tubes of the confirmation medium are inoculated with the cultures from the tubes of double-strength selective enrichment medium, and with the cultures from the tubes of single-strength selective enrichment medium in which gas
41、formation or opacity preventing the detection of gas formation has been noted.4.2.5The tubes from 4.2.4 are incubated at 30 C or 37 C (as agreed) for 24 h or 48 h and the tubes are examined for gas formation.4.2.6The most probable number of coliforms per millilitre or per gram of sample (i.e. the MP
42、N) is calculated from the number of tubes in the new series (4.2.5) showing gas formation. A table for determination of most probable numbers is used.www.standards.org.au Standards Australia5Culture media and diluents5.1GeneralSee ISO 7218, ISO/TS 11133-1 and ISO/TS 11133-2 for the preparation, prod
43、uction and performance testing of culture media.5.2DiluentsSee ISO 6887 (relevant part), ISO 8261 or the specific International Standard dealing with the product under examination.5.3Selective enrichment medium: Lauryl sulfate tryptose broth5.3.1Compositiona) Double-strength mediumb) Single-strength
44、 mediumEnzymatic digest of milk and animal proteins40 g20 gLactose (C12H22O11H2O)10 g5 gDipotassium hydrogen phosphate (K2HPO4)5,5 g2,75 gPotassium dihydrogen phosphate (KH2PO4)5,5 g2,75 gSodium chloride10 g5 gSodium lauryl sulfate0,2 g0,1 gWater1 000 ml1 000 ml5.3.2PreparationDissolve the different
45、 components or the dehydrated complete medium in the water, by heating if necessary. Adjust the pH, if necessary, so that after sterilization it is 6,8 0,2 at 25 C.Dispense the media in quantities of 10 ml into tubes of dimensions of approximately 16 mm 160 mm (6.4)containing Durham tubes (6.5) in t
46、he case of single-strength medium, and into test tubes of dimensions ofapproximately 20 mm 200 mm (6.4) not containing Durham tubes (6.5) in the case of the double-strengthmedium.Sterilize in an autoclave set at 121 C for 15 min. The Durham tubes shall not contain air bubbles after sterilization.5.3
47、.3Performance testing for the quality assurance of the culture mediumFor the definitions of selectivity and productivity, refer to ISO/TS 11133-1. Performance testing relating to lauryl sulfate tryptose broth is given in ISO/TS 11133-2:2003, Table B.1.The Standard is downloaded from Standard Sharing