SIST EN ISO 7704:2023
(Main)Water quality - Requirements for the performance testing of membrane filters used for direct enumeration of microorganisms by culture methods (ISO 7704:2023)
Water quality - Requirements for the performance testing of membrane filters used for direct enumeration of microorganisms by culture methods (ISO 7704:2023)
This International Standard specifies requirements for the evaluation of membrane filters intended for the concentration for direct enumeration of specific microorganisms and mixed populations. These requirements are applicable to all membrane filters intended for the microbiological analysis of all kinds of water and other liquid samples.
These requirements are intended for the test to demonstrate the suitability of the whole system - membrane filter together with culture medium including the filtration step - required for specific tests described in International Standards.
The membrane filters required for use are described in each specific standard. This International Standard applies to producers and users such as:
— commercial bodies producing and/or distributing membrane filters;
— non-commercial bodies supplying membrane filters to third parties;
— microbiological laboratories using membrane filters for their own testing or providing these to other users.
Wasserbeschaffenheit - Anforderungen für die Bewertung von Membranfiltern zur direkten Zählung mittels mikrobiologischer Kulturverfahren (ISO 7704:2023)
Dieses Dokument legt die Anforderungen an die Leistungsprüfung von Membranfiltern fest, die für die Rückhaltung und die anschließende direkte Zählung von Mikroorganismen durch Verfahren zur Kultivierung verwendet werden.
Dieses Dokument gilt für Membranfilter, die für die Rückhaltung und anschließende direkte Zählung bestimmter Mikroorganismen auf festen Medien oder auf anderen Vorrichtungen, die Medien enthalten, wie absorbierendes Trägermaterial, verwendet werden [19].
Dieses Dokument gilt nicht für Membranfilter, die zur Aufkonzentrierung und Elution oder für qualitative Verfahren verwendet werden.
Die Prüfungen gelten für Membranfilter, die für die mikrobiologische Analyse verschiedener Arten von Wasser bestimmt sind, wie:
Trinkwasser, in Flaschen abgefülltes Wasser und andere Arten von Wasser mit voraussichtlich geringer Anzahl von Mikroorganismen;
Wasser mit einer erwarteten höheren Anzahl von Mikroorganismen, z. B. Oberflächenwasser und Prozesswasser.
Die Prüfungen sollen die Eignung des gesamten Systems (Membranfilter zusammen mit dem Nährmedium einschließlich der Filtrationsstufe) nachweisen, die für die in den Literaturhinweisen [3] [6] [8] [10] [12] und [13] beschriebenen spezifischen Prüfungen erforderlich ist.
Dieses Dokument gilt für:
Hersteller, die Membranfilter produzieren;
Laboratorien für Mikrobiologie, die Membranfilter für ihre eigenen Prüfungen verwenden oder diese an andere Endanwender liefern.
Qualité de l'eau - Exigences relatives aux essais de performance des membranes filtrantes utilisées pour le dénombrement direct des micro-organismes par des méthodes de culture (ISO 7704:2023)
Le présent document spécifie les exigences pour les essais de performance des membranes filtrantes utilisées pour la rétention suivie d'un dénombrement direct des micro-organismes par des méthodes de culture.
Le présent document s'applique aux membranes filtrantes qui sont utilisées pour la rétention suivie d'un dénombrement direct de micro-organismes spécifiques sur des milieux solides ou sur d'autres dispositifs contenant des milieux, comme des pads en papier absorbants [19].
Le présent document ne s'applique pas aux membranes filtrantes utilisées pour la concentration et l'élution ou pour des méthodes qualitatives.
Les essais s'appliquent aux membranes filtrantes destinées à l'analyse microbiologique de différents types d'eau, tels que:
— l'eau potable, l'eau embouteillée et d'autres types d'eau dans laquelle un faible nombre de micro-organismes est attendu;
— l'eau dans laquelle un plus grand nombre de micro-organismes est attendu, par exemple l'eau de surface et l'eau de process.
Ces essais sont destinés à démontrer l'adéquation de l'ensemble du système (membrane filtrante et milieu de culture, y compris l'étape de filtration) requis pour les essais spécifiques décrits dans les Références [3], [6], [8], [10], [12] et [13].
Le présent document s'applique:
— aux fabricants produisant des membranes filtrantes;
— aux laboratoires de microbiologie utilisant des membranes filtrantes pour leurs propres essais ou les fournissant à d'autres utilisateurs finaux.
Kakovost vode - Zahteve za preskušanje lastnosti membranskih filtrov, ki se uporabljajo za štetje mikroorganizmov z metodami kultivacije (ISO 7704:2023)
Ta mednarodni standard določa zahteve za oceno membranskih filtrov za koncentriranje za neposredno štetje specifičnih mikroorganizmov in mešanih populacij. Te zahteve veljajo za vse membranske filtre, namenjene za mikrobiološko analizo vseh vrst vzorcev vode in drugih tekočin. Te zahteve so namenjene za preskus, s katerim se dokaže ustreznost celotnega sistema – membranski filter z medijem za gojenje kulture, vključno s fazo filtriranja – potrebnega za določene preskuse, opisane v mednarodnih standardih. Mehanski filtri, zahtevani za uporabo, so opisani v posameznih standardih. Ta mednarodni standard se uporablja za proizvajalce in uporabnike, kot so: – komercialni organi, ki proizvajajo in/ali distribuirajo membranske filtre;
– nekomercialni organi, ki membranske filtre dobavljajo tretjim strankam;
– mikrobiološki laboratoriji, ki uporabljajo membranske filtre za lastno preskušanje ali jih zagotavljajo drugim uporabnikom.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 7704:2023
01-junij-2023
Kakovost vode - Zahteve za preskušanje lastnosti membranskih filtrov, ki se
uporabljajo za štetje mikroorganizmov z metodami kultivacije (ISO 7704:2023)
Water quality - Requirements for the performance testing of membrane filters used for
direct enumeration of microorganisms by culture methods (ISO 7704:2023)
Wasserbeschaffenheit - Anforderungen für die Bewertung von Membranfiltern zur
direkten Zählung mittels mikrobiologischer Kulturverfahren (ISO 7704:2023)
Qualité de l'eau - Exigences relatives aux essais de performance des membranes
filtrantes utilisées pour le dénombrement direct des micro-organismes par des méthodes
de culture (ISO 7704:2023)
Ta slovenski standard je istoveten z: EN ISO 7704:2023
ICS:
07.100.20 Mikrobiologija vode Microbiology of water
SIST EN ISO 7704:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 7704:2023
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SIST EN ISO 7704:2023
EN ISO 7704
EUROPEAN STANDARD
NORME EUROPÉENNE
January 2023
EUROPÄISCHE NORM
ICS 07.100.20
English Version
Water quality - Requirements for the performance testing
of membrane filters used for direct enumeration of
microorganisms by culture methods (ISO 7704:2023)
Qualité de l'eau - Exigences relatives aux essais de Wasserbeschaffenheit - Anforderungen für die
performance des membranes filtrantes utilisées pour Bewertung von Membranfiltern zur direkten Zählung
le dénombrement direct des micro-organismes par des mittels mikrobiologischer Kulturverfahren (ISO
méthodes de culture (ISO 7704:2023) 7704:2023)
This European Standard was approved by CEN on 19 November 2022.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 7704:2023 E
worldwide for CEN national Members.
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SIST EN ISO 7704:2023
EN ISO 7704:2023 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 7704:2023
EN ISO 7704:2023 (E)
European foreword
This document (EN ISO 7704:2023) has been prepared by Technical Committee ISO/TC 147 "Water
quality" in collaboration with Technical Committee CEN/TC 230 “Water analysis” the secretariat of
which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by July 2023, and conflicting national standards shall be
withdrawn at the latest by July 2023.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 7704:2023 has been approved by CEN as EN ISO 7704:2023 without any modification.
3
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SIST EN ISO 7704:2023
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SIST EN ISO 7704:2023
INTERNATIONAL ISO
STANDARD 7704
Second edition
2023-01
Water quality — Requirements for
the performance testing of membrane
filters used for direct enumeration of
microorganisms by culture methods
Qualité de l'eau — Exigences relatives aux essais de performance
des membranes filtrantes utilisées pour le dénombrement direct des
micro-organismes par des méthodes de culture
Reference number
ISO 7704:2023(E)
© ISO 2023
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SIST EN ISO 7704:2023
ISO 7704:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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SIST EN ISO 7704:2023
ISO 7704:2023(E)
Contents Page
Foreword .v
Introduction .vii
1 S c op e . 1
2 Nor m at i ve r ef er enc e s . 1
3 T erms and definitions . 1
3.1 G eneral terminology . 2
3.2 T erminology of performance testing . 3
3.3 T erminology for test microorganisms . 4
4 P r i nc iple . 5
4.1 General . 5
4 .1.1 I nt r o duc t ion . 5
4.1.2 Batch testing . 6
4.1.3 Supplementary testing . 6
4.2 P erformance testing . 7
4.2.1 M odules for batch and supplementary testing . 7
4.2.2 A bsence of microbial contamination . 7
5 A pparatus and glassware .8
6 C ulture media and diluents .8
7 P reparation of microorganisms for performance testing . 8
7.1 G eneral . 8
7. 2 R ef er enc e c ou nt . 8
7.2.1 Q uantitative productivity testing . 8
7.2.2 Q ualitative selectivity testing . 9
7.2.3 Qualitative specificity testing . 9
7.3 P reparation of a standardized test suspension using a working culture . 9
7.3.1 General . 9
7.3.2 Preparation of the working culture . 9
7.3.3 Preparation of a standardized test suspension (inoculum) for the test . 10
7.4 P reparation of a test suspension using reference material . 10
8 S ampling of membrane filters for testing .10
9 P rocedure .11
9.1 G eneral . 11
9.2 I noculation by spread plate technique . 11
9.2.1 G eneral . 11
9.2.2 Inoculation .12
9.3 I noculation by membrane filtration technique .12
9.3.1 General .12
9.3.2 Inoculation .12
9.4 I ncubation and counting . 13
9.5 T est for absence of microbial contamination . 13
10 C alculation, expression and interpretation of results .13
10.1 G eneral .13
10.2 P roductivity testing . 13
10.3 S electivity testing . 14
10.4 S pecificity testing . 14
11 Documentation of test results .14
11.1 Te s t r ep or t . 14
11.2 I nformation provided by the manufacturer . 15
11.3 T raceability . 15
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SIST EN ISO 7704:2023
ISO 7704:2023(E)
Annex A (normative) Diagram of the procedure for batch testing .16
Annex B (informative) Example of a card for recording test results from batch testing .17
Annex C (informative) Quantitative supplementary testing of membrane filters .18
Annex D (informative) Qualitative supplementary testing of membrane filters .21
Annex E (informative) Practical example of quantitative batch testing and quantitative
supplementary testing by the end user .25
Bibliography .35
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SIST EN ISO 7704:2023
ISO 7704:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 4,
Microbiological methods, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 230, Water analysis, in accordance with the Agreement on technical
cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 7704:1985), which has been technically
revised.
The main changes are as follows:
— the scope has been changed to cover the requirements for the performance testing of membrane
filters used for retention and direct enumeration;
— clauses have been added for terms and definitions, microorganisms, sampling and replicates,
procedure, inoculation and incubation, counting, calculation and documentation;
— the clauses referencing to culture media and diluents, test strain preparation, performance testing
and procedure have been revised to align with ISO 8199 and ISO 11133;
— Annex A has been added with a diagram of the batch testing;
— Annex B has been added to give an example of a card to record the test results from batch testing
and supplementary testing of membrane filters;
— Annex C has been added to describe the quantitative additional testing of membrane filters including
a diagram of the procedure;
— Annex D has been added to describe the qualitative supplementary testing of membrane filters;
— Annex E has been added to give a practical example of batch testing and quantitative additional
testing by the end user including a diagram of the procedure;
— the Bibliography has been added.
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SIST EN ISO 7704:2023
ISO 7704:2023(E)
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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SIST EN ISO 7704:2023
ISO 7704:2023(E)
Introduction
In laboratories carrying out microbiological examinations, the main objectives are to either capture,
resuscitate, grow, detect or enumerate, or all, a wide variety of microorganisms. Membrane filters are
used in many traditional microbiological culture techniques and are commercially available in various
brands and types. Many comparison studies of membrane filters which have been reported in the
literature show differences in their ability to recover bacteria from water samples, see References [22],
[23], [28], [30], [31], [32], [33] and [34]. The complex manufacturing process means that the chemical
composition, pore size and pore structure can vary, depending on the brands, and even on the lot of
material. Furthermore, the manufacturing process can also release leachables that can potentially
interfere with the recovery of microorganisms.
Thus, it is very important to standardize the performance testing of membrane filters as much as
possible, not only to provide consistent results, but also to enable the development of standardized
procedures for enumerating specific microorganisms.
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SIST EN ISO 7704:2023
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SIST EN ISO 7704:2023
INTERNATIONAL STANDARD ISO 7704:2023(E)
Water quality — Requirements for the performance
testing of membrane filters used for direct enumeration of
microorganisms by culture methods
1 S cope
This document specifies the requirements for the performance testing of membrane filters used for the
retention followed by direct enumeration of microorganisms by culture methods.
This document is applicable to membrane filters which are used for retention followed by direct
enumeration of specific microorganisms on solid media or on other devices containing media, like
[19]
absorbent pads .
This document is not applicable for membrane filters used for concentration and elution or for
qualitative methods.
These tests are applicable to the membrane filters intended for the microbiological analysis of different
types of water, such as:
— drinking water, bottled water and other types of water with expected low numbers of
microorganisms;
— water with expected higher numbers of microorganisms, for example, surface water and process
water.
These tests are intended to demonstrate the suitability of the whole system (membrane filter together
with the culture medium including the filtration step) required for the specific tests described in
References [3], [6], [8], [10], [12] and [13].
This document applies to:
— manufacturers producing membrane filters;
— microbiological laboratories using membrane filters for their own testing or providing these to
other end users.
2 Normat ive references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 8199:2018, Water quality — General requirements and guidance for microbiological examinations by
culture
ISO 11133:2014, Microbiology of food, animal feed and water — Preparation, production, storage and
performance testing of culture media
ISO 11133:2014/Amd1: 2018, Microbiology of food, animal feed and water — Preparation, production,
storage and performance testing of culture media
3 T erms and definitions
For the purposes of this document, the following terms and definitions apply.
1
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SIST EN ISO 7704:2023
ISO 7704:2023(E)
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 General terminolo gy
3.1.1
membrane filter
porous hydrophilic filtration matrix, composed of different polymers with filtration characteristics
equivalent to its/their rated nominal pore sizes, typically ranging from 0,1 µm to 1,2 µm, which is
intended to be used for the retention of microorganisms
Note 1 to entry: The membrane filter ensures the effective retention of microorganisms depending on the
membrane pore size when a differential (positive or negative) pressure is applied.
Note 2 to entry: The type of membrane filter to be used for a certain microbiological method is described in the
corresponding specific standard (3.1.7).
3.1.2
culture medium
formulation of substances, in liquid, semi-solid or solid form, which contain either natural and/
or synthetic constituents intended to support the multiplication (with or without constituents for
inhibition of certain microorganisms), identification or preservation of viability of microorganisms
Note 1 to entry: The culture medium to be used for a certain microbiological method is described in the
corresponding specific standard (3.1.7), see specific culture medium (3.1.3).
[SOURCE: ISO 11133:2014, 3.3.1, modified — “constituents for” has been included and Note 1 to entry
has been replaced.]
3.1.3
specific culture medium
culture medium (3.1.2), usually selective, as designated in a specific standard (3.1.7) for use with
membrane filters (3.1.1)
[8]
EXAMPLE 1 Chromogenic coliform agar (CCA) used with membrane filters in accordance with ISO 9308-1 .
[6]
EXAMPLE 2 Slanetz and Bartley medium used with membrane filters in accordance with ISO 7899-2 .
3.1.4
reference medium
culture medium (3.1.2), usually non-selective, for determination of the reference count (3.3.8) and
supplementary quantitative testing (3.2.2)
Note 1 to entry: The reference medium is usually a non-selective culture medium (3.1.2), which is different to the
culture medium under test and has been demonstrated to be suitable for use in the performance testing.
EXAMPLE Tryptone soya agar (TSA) is in accordance with ISO 11133.
[SOURCE: ISO 11133:2014, 3.3.4.13, modified — Note 1 to entry has been added and "is in accordance
with ISO 11133" has been added in the example.]
3.1.5
batch of membrane filter
lot of membrane filter
homogeneous and fully traceable units of membrane filter (3.1.1) referring to a defined amount of bulk,
semi-finished product or end product, which is consistent in type and quality, and which has been
produced within one defined production period, having been assigned the same batch (or lot) number
2
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SIST EN ISO 7704:2023
ISO 7704:2023(E)
3.1.6
batch of culture medium
lot of culture medium
homogeneous and fully traceable units of a culture medium (3.1.2) referring to a defined amount of
bulk, semi-finished product or end product, which is consistent in type and quality, and which has been
produced within one defined production period, having been assigned the same batch (or lot) number
Note 1 to entry: If the user does not define the batch or lot of culture medium used for performance testing of
membrane filters as the “end product”, it is important to demonstrate that the production process is sufficiently
controlled to produce culture media of consistent quality (e.g. by monitoring culture media performance testing
results).
[SOURCE: ISO 11133:2014, 3.1.2, modified — "medium" has been changed to "culture medium" and
Note 1 to entry has been added.]
3.1.7
specific standard
International Standard or guidance document describing the microbiological analysis of different types
of water for the detection or enumeration of a specific microorganism (or group of microorganisms)
3.2 T erminology of performance testing
3.2.1
batch testing
test of units of membrane filters (3.1.1) from a batch of membrane filter (3.1.5) for its/their intended use
with the specific culture medium (3.1.3) and determination of reference count (3.3.6)
3.2.2
supplementary quantitative testing
test of units of membrane filters (3.1.1) from a batch of membrane filter (3.1.5) for its/their intended use
with the specific culture medium (3.1.3), determination of reference count (3.3.6), test of the membrane
filters on a non-selective culture medium and test of the culture medium without membrane filter
Note 1 to entry: Annex C gives detailed description of the supplementary quantitative testing.
Note 2 to entry: Supplementary quantitative testing is used when a new type of a membrane filter(s) (3.1.1), or a
new manufacturer is tested initially, or when a problem in the day-to-day use or batch testing (3.2.1) of membrane
filters is noticed.
3.2.3
performance of the membrane filter
response of a membrane filter (3.1.1) challenged by a test organism (3.3.3) under define
...
SLOVENSKI STANDARD
oSIST prEN ISO 7704:2021
01-november-2021
[Not translated]
Water quality - Requirements for the performance testing of membrane filters used for
direct enumeration of microorganisms by culture methods (ISO/DIS 7704:2021)
Wasserbeschaffenheit - Anforderungen für die Bewertung von Membranfiltern zur
direkten Zählung mittels mikrobiologischer Kulturverfahren (ISO/DIS 7704:2021)
Qualité de l'eau - Évaluation des membranes filtrantes utilisées pour des analyses
microbiologiques (ISO/DIS 7704:2021)
Ta slovenski standard je istoveten z: prEN ISO 7704
ICS:
07.100.20 Mikrobiologija vode Microbiology of water
oSIST prEN ISO 7704:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN ISO 7704:2021
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oSIST prEN ISO 7704:2021
DRAFT INTERNATIONAL STANDARD
ISO/DIS 7704
ISO/TC 147/SC 4 Secretariat: DIN
Voting begins on: Voting terminates on:
2021-10-07 2021-12-30
Water quality — Requirements for the performance
testing of membrane filters used for direct enumeration of
microorganisms by culture methods
ICS: 07.100.20
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
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oSIST prEN ISO 7704:2021
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oSIST prEN ISO 7704:2021
ISO/DIS 7704:2021(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General terms and definitions . 2
3.2 Terminology of performance testing . 3
3.3 Terminology for test microorganisms . 4
4 Principle . 6
4.1 General . 6
4.1.1 Batch testing . 6
4.1.2 Supplementary testing. 7
4.2 Testing procedures . 7
4.2.1 Microbiological methods . 7
4.2.2 Absence of microbial contamination . 8
5 Apparatus and glassware . 8
6 Culture media and diluents . 8
7 Preparation of microorganisms for performance testing . 8
7.1 General . 8
7.2 Reference count . 9
7.2.1 Quantitative productivity testing. 9
7.2.2 Qualitative selectivity testing .10
7.2.3 Qualitative specificity testing .10
7.3 Preparation of a standardized test suspension using a working culture .10
7.3.1 Preparation of the test suspension (inoculum) for the test . .10
7.4 Preparation of a test suspension using reference material .11
8 Sampling of membrane filters for testing.11
9 Procedure.11
9.1 General .11
9.2 Inoculation by spread plate technique .12
9.2.1 General.12
9.2.2 Inoculation .12
9.3 Inoculation by membrane filtration technique .12
9.3.1 General.12
9.3.2 Inoculation .13
9.4 Incubation and counting .13
9.5 Test on absence of microbial contamination .13
10 Calculation, expression and interpretation of results .13
10.1 General .13
10.2 Productivity testing .14
10.3 Selectivity testing .14
10.4 Specificity testing .14
11 Documentation of test results .15
11.1 General .15
11.2 Information provided by the manufacturer .15
11.3 Traceability .15
Annex A (normative) Diagram of the batch testing .16
Annex B (informative) Example of card for recording test results from batch testing .17
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Annex C (informative) Quantitative supplementary testing of membrane filters .18
Annex D (informative) Qualitative supplementary testing of membrane filters .20
Annex E (informative) Practical example of quantitative batch testing and quantitative
supplementary testing by the end user .24
Bibliography .33
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oSIST prEN ISO 7704:2021
ISO/DIS 7704:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 4,
Microbiological methods.
This second edition cancels and replaces the first edition (ISO 7704:1985), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the scope has been changed to cover the requirements for the performance testing of membrane
filters used for retention and direct enumeration;
— clauses have been added for terms and definitions, microorganisms, sampling and replicates,
procedure, inoculation and incubation, counting, calculation and documentation;
— the clauses referencing culture media and diluents, test strain preparation, performance testing
and procedure have been revised to align with ISO 8199 and ISO 11133;
— Annex B has been added to give an example of card for recording test results from batch testing and
supplementary testing of membrane filters;
— Annex C has been added to describe the quantitative additional testing of membrane filters;
— Annex D has been added to describe the qualitative supplementary testing of membrane filters;
— Annex E has been added to give a practical example of batch testing and quantitative additional
testing by the end user;
— Bibliography has been added;
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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oSIST prEN ISO 7704:2021
ISO/DIS 7704:2021(E)
Introduction
This document describes the performance testing of membrane filters used for retention followed by
direct enumeration of microorganisms by culture methods.
The main changes listed in the foreword, introduced in this document compared to ISO 7704:1985, are
considered as major.
In laboratories carrying out microbiological examinations, the main objectives are to capture,
resuscitate, grow, detect and/or enumerate a wide variety of microorganisms. Membrane filters are
used in many traditional microbiological culture techniques and are commercially available in various
brands and types. Many comparison studies of membrane filters which have been reported in the
literature show differences in their ability to recover bacteria from water samples, see References.
[18],[19],[23],[25],[27],[28],[29],[30] The complex manufacturing process means that the chemical
composition, pore size and pore structure can vary, depending on the brands, and even on the lot of
material. Furthermore, the manufacturing process can also release leachables that can potentially
interfere with the recovery of microorganisms.
Thus, it is very important to standardize the performance testing of membrane filters as much as
possible, not only to provide consistent results, but also to enable the development of standardized
procedures for enumerating specific microorganisms.
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oSIST prEN ISO 7704:2021
DRAFT INTERNATIONAL STANDARD ISO/DIS 7704:2021(E)
Water quality — Requirements for the performance
testing of membrane filters used for direct enumeration of
microorganisms by culture methods
1 Scope
This document specifies the requirements for the performance testing of membrane filters. This
concerns membrane filters which are used for retention followed by direct enumeration of specific
[16]
microorganisms on solid media or on other devices containing media, like absorbent pads .
It is not applicable for membrane filters used for concentration and elution or for qualitative methods.
These tests are applicable to membrane filters intended for the microbiological analysis of different
types of water, like:
— drinking water, bottled water and other types of water with expected low numbers of
microorganisms;
— water with expected higher numbers of microorganisms, for example surface water and process
water.
These tests are intended to demonstrate the suitability of the whole system - membrane filter
together with culture medium including the filtration step - required for the specific tests described in
International Standards.
This document applies to:
— manufacturers producing membrane filters;
— microbiological laboratories using membrane filters for their own testing or providing these to
other end users.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 8199:2018, Water quality — General requirements and guidance for microbiological examinations by
culture
I S O 11133:2014/A M D1: 2018 , Microbiology of food, animal feed and water — Preparation, production,
storage and performance testing of culture media
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http:// www .iso .org ./ obp
— IEC Electropedia: available at https:// www .electropedia .org/
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oSIST prEN ISO 7704:2021
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3.1 General terms and definitions
3.1.1
membrane filter(s)
porous hydrophilic filtration matrix, composed of different polymers with filtration characteristics
equivalent to its/their rated nominal pore sizes, typically ranging from 0,1 µm to 1,2 µm, which is
intended to be used for retention of microorganisms
Note 1 to entry: The membrane filter assures the effective retention of microorganisms depending on the
membrane pore size when a differential (positive or negative) pressure is applied.
Note 2 to entry: The type of membrane filter to be used for a certain microbiological method is described in the
corresponding specific standard (3.1.7).
3.1.2
culture medium
formulation of substances, in liquid, semi-solid or solid form, which contain natural and/or synthetic
constituents intended to support the multiplication (with or without constituents for inhibition of
certain microorganisms), identification or preservation of viability of microorganisms
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.3.1, modified — “constituents for” included and
Note 1 to entry has been deleted.]
Note 1 to entry: The culture medium to be used for a certain microbiological method is described in the
corresponding specific standard (3.1.7), see specific culture medium (3.1.3).
3.1.3
specific culture medium
culture medium (3.1.2), usually selective, as designated in a specific standard (3.1.7) for use with
membrane filters (3.1.1)
[7]
EXAMPLE Chromogenic Coliform Agar (CCA) used with membrane filters in accordance with ISO 9308-1 ;
[5]
Slanetz and Bartley medium used with membrane filters in accordance with ISO 7899-2 .
3.1.4
reference medium
culture medium (3.1.2) for comparative supplementary performance testing
Note 1 to entry: The reference medium is usually a non-selective culture medium (3.1.2), which is different to the
culture medium under test and demonstrated to be suitable for use in the performance testing.
EXAMPLE Tryptone soya agar (TSA) is in accordance with ISO 11133:2014/AMD1: 2018/ AMD2: 2020.
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.3.4.13, modified — Note 1 to entry has been
implemented.]
3.1.5
batch of membrane filters
lot of membrane filters
homogeneous and fully traceable units of membrane filter (3.1.1) referring to a defined amount of bulk,
semi-finished product or end product, which is consistent in type and quality and which has been
produced within one defined production period, having been assigned the same batch (or lot) number
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oSIST prEN ISO 7704:2021
ISO/DIS 7704:2021(E)
3.1.6
batch of culture medium
lot of culture medium
homogeneous and fully traceable units of a culture medium (3.1.2) referring to a defined amount of
bulk, semi-finished product or end product, which is consistent in type and quality and which has been
produced within one defined production period, having been assigned the same batch (or lot) number
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.1.2, modified — reference to 3.1.2 has been
added.]
Note 1 to entry: If the user does not define the batch or lot of culture medium used for performance testing of
membrane filters as the “end product”, it is important to demonstrate that the production process is sufficiently
controlled to produce culture media of consistent quality (for example by monitoring culture media performance
testing results).
3.1.7
specific standard
International Standard or guidance document describing the microbiological analysis of different types
of water for the detection or enumeration of a specific microorganism (or group of microorganisms)
[SOURCE: ISO 6887-1:2017, 3.10, modified]
3.2 Terminology of performance testing
3.2.1
batch testing
test of units of membrane filters (3.1.1) from a batch or a lot (3.1.5) for its/their intended use with the
specific culture medium (3.1.3) and determination of reference count (3.3.6)
3.2.2
supplementary quantitative testing
test of units of membrane filters (3.1.1) from a batch or a lot (3.1.5) for its/their intended use with the
specific culture medium (3.1.3); determination of reference count (3.3.6); test of the membrane filters on
a non-selective culture medium and test of the culture medium without membrane filter
Note 1 to entry: A detailed description of the supplementary quantitative testing is given in Annex C.
Note 2 to entry: Supplementary quantitative testing is used when a new type of a membrane filter(s) (3.1.1), or
a new manufacturer is tested initially, or when a problem in the day-to-day use or batch testing of membrane
filters is noticed.
3.2.3
performance of membrane filter
response of a membrane filter (3.1.1) challenged by a test organism (3.3.1) under defined conditions
Note 1 to entry: The defined conditions are described in the specific standard (3.1.7) for the intended use of
the membrane filter (3.1.1), like: test organism (3.3.1), specific culture medium (3.1.3), reference medium (3.1.4),
productivity (3.2.7), selectivity (3.2.6), incubation time and temperature.
3.2.4
performance of culture medium
response of a culture medium (3.1.2) challenged by a test organism (3.3.1) under defined conditions
[S OU RC E: I S O 11133:2014/A M D1: 2018/ A M D2: 2020, 3 . 2 .1]
3.2.5
productivity
level of recovery of a target microorganism (3.2.5) on the culture medium (3.1.2) with the membrane
filter (3.1.1) under defined conditions
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.2.4, modified — adapted to the performance
testing of membrane filters.]
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oSIST prEN ISO 7704:2021
ISO/DIS 7704:2021(E)
3.2.6
selectivity
degree of inhibition of a non-target microorganism (3.2.6) on a selective culture medium (3.1.2) with the
membrane filter (3.1.1) under defined conditions
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.2.5, modified — adapted to the performance
testing of membrane filters.]
3.2.7
electivity
specificity
demonstration, under defined conditions, that a non-target microorganism (3.2.6), if able to grow on
the medium, does not show the same visual characteristics as the target microorganisms (3.2.5) on the
culture medium (3.1.2) with membrane filter (3.1.1) under defined conditions
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.2.6, modified — adapted to the performance
testing of membrane filters.]
3.3 Terminology for test microorganisms
3.3.1
target microorganism
microorganism or group of microorganisms to be detected or enumerated which should be expected
to grow under defined conditions[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.2.2] , modified
3.3.2
non-target microorganism
microorganism that is suppressed by the medium and/or conditions of incubation or does not show
expected characteristics of the target microorganism
[S OU RC E: I S O 11133:2014/A M D1: 2018/ A M D2: 2020, 3 . 2 . 3]
3.3.3
test microorganism
control strain
microorganism generally used for performance testing of membrane filters (3.1.1) and/or culture media
(3.1.2)
Note 1 to entry: Test microorganisms / control strains are further defined in accordance with their source (see
3.3.2 to 3.3.8).
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.4.1, modified — adapted to the performance
testing of membrane filters.]
3.3.4
reference strain
microorganism obtained directly from a reference culture collection and defined to at least the species
level
Note 1 to entry: A reference culture collection is a culture collection which is a member of the World Federation
of Culture Collections (WFCC) or the European Culture Collections’ Organisation (ECCO).
Note 2 to entry: A reference strain is catalogued and described according to its characteristics and preferably
originating from water as applicable.
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.4.2, modified — Note 1 and 2 to entry have been
implemented using modified text from shortened definition.]
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3.3.5
reference stock
set of separate identical cultures obtained by a single subculture from the reference strain (3.3.4) either
in the laboratory or from a supplier
[S OU RC E: I S O 11133:2014/A M D1: 2018/ A M D2: 2020, 3 .4 . 3]
3.3.6
stock culture
primary subculture from a reference stock (3.3.5)
[S OU RC E: I S O 11133:2014/A M D1: 2018/ A M D2: 2020, 3 .4 .4]
3.3.7
working culture
subculture from a reference stock (3.3.5) or stock culture (3.3.6) or a reference material (3.3.9) or a
certified reference material (3.3.10)
Note 1 to entry: Multi-strain reference material (3.3.9) and multi-strain certified reference material (3.3.10) can
also be used for the preparation of working cultures.
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.4.4, modified — Note 1 to entry has been added.]
3.3.8
reference count
total count of colonies on a mostly non-selective culture medium (3.1.2) obtained without usage of a
membrane filter (3.1.1)
Note 1 to entry: For this the term “inoculum level” is often used.
3.3.9
reference material
RM
microbiological material containing a quantity of revivable microorganisms, sufficiently homogenous
and stable with respect to the quantity of revivable microorganisms, which has been established to be
fit for its intended use in a measurement process
[12]
Note 1 to entry: See ISO Guide 30 .
[SOURCE: ISO 11133:2014/AMD1: 2018/ AMD2: 2020, 3.4.6, modified — Note 1 to entry: reference has
been updated.]
Not
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