|
International
Standard
ISO 6887-1
Second edition
Microbiology of the food chain —
2017-03
Preparation of test samples, initial
suspension and decimal dilutions
AMENDMENT 1
for microbiological examination —
2024-07
Part 1:
General rules for the preparation of
the initial suspension and decimal
dilutions
AMENDMENT 1: Requirements and
guidance on the use of a larger test
portion size for qualitative methods
Microbiologie de la chaîne alimentaire — Préparation des
échantillons, de la suspension mère et des dilutions décimales en
vue de l'examen microbiologique —
Partie 1: Règles générales pour la préparation de la suspension
mère et des dilutions décimales
AMENDEMENT 1: Exigences et recommandations sur l’utilisation
d’une taille de prise d’essai plus grande pour les méthodes
qualitatives
Reference number
ISO 6887-1:2017/Amd.1:2024(en) © ISO 2024
ISO 6887-1:2017/Amd.1:2024(en)
© ISO 2024
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: [email protected]
Website: www.iso.org
Published in Switzerland
ii
ISO 6887-1:2017/Amd.1:2024(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 34, Food products, Subcommittee SC 9,
Microbiology, in collaboration with the European Committee for Standardization (CEN) Technical Committee
CEN/TC 463, Microbiology of the food chain, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
A list of parts in the ISO 6887 series can be found on the ISO website.
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.
iii
ISO 6887-1:2017/Amd.1:2024(en)
Microbiology of the food chain — Preparation of test samples,
initial suspension and decimal dilutions for microbiological
examination —
Part 1:
General rules for the preparation of the initial suspension
and decimal dilutions
AMENDMENT 1: Requirements and guidance on the use of a larger
test portion size for qualitative methods
Clause 2
Add the following normative references:
ISO 16140-4:2020, Microbiology of the food chain — Method validation — Part 4: Protocol for method validation
in a single laboratory
ISO 16140-4:2020/Amd 1:2024, Microbiology of the food chain — Method validation — Part 4: Protocol for method
validation in a single laboratory — Amendment 1: Validation of a larger test portion size for qualitative methods
3.2
Replace the text with the following:
3.2
composite sample
mixed sample of a number of the same items (3.13) of food, animal feed, animals or environment, prepared
in or out of the laboratory from which a test portion is taken for examination
Note 1 to entry: See Figure A.1 for an illustration of a composite sample.
3.3
Replace the text with the following:
3.3
pooled sample
mixed sample of a number of the same items (3.13) of food, animal feed, animals or environment, prepared
in or out of the laboratory where the complete mixture is the test portion and is taken as a whole for
examination
Note 1 to entry: See Figure A.1 for an illustration of a pooled sample
Add the following terminological entries:
ISO 6887-1:2017/Amd.1:2024(en)
3.11
category
group of sample types (3.12) of the same origin
Note 1 to entry: Food categories are listed in ISO 16140-2:2016, Table A.1.
EXAMPLE Heat-processed milk and dairy products.
[SOURCE: ISO 16140-1:2016, 2.11, modified — Note 1 to entry added.]
3.12
type
for a given category (3.11), a group of items (3.13) processed in a similar way, with similar intrinsic
characteristics and a similar microbial ecology
Note 1 to entry: Food types are listed in ISO 16140-2:2016, Table A.1.
EXAMPLE Food category: heat-processed milk and dairy products; food type: pasteurized dairy product.
[SOURCE: ISO 16140-1:2016, 2.78, modified — Note 1 to entry added.]
3.13
item
single specified food, feed, environmental or primary production matrix
Note 1 to entry: Examples for food items are listed in ISO 16140-2:2016, Table A.1.
EXAMPLE Food category: heat-processed milk and dairy products; food type: pasteurized dairy product; food
item: milk-based desserts.
[SOURCE: ISO 16140-1:2016, 2.34, modified — Note 1 to entry added.]
3.14
larger test portion
measured (volume or mass) representative sample taken from the laboratory sample (3.1) or test sample
(3.4) for use in the preparation of the initial suspension that is larger than the test portion that has been
described in the original method and/or validation document
9.3
Replace the text with the following:
9.3 Composite sample and larger test portion
9.3.1 Composite sample
A composite sample is where a number of the same items are mixed, and a test portion is taken for
examination in the laboratory as illustrated in Figure A.1. The size of the test portion removed from the
composite sample will remain the same as described in the original method and/or validation document.
Compositing shall be applicable to qualitative tests only.
A number of items may be composited at the sampling stage by the client (out of the laboratory) or by the
laboratory (at client’s request). Only items from the same origin or source (e.g. same batch or lot) shall be
composited.
ISO 6887-1:2017/Amd.1:2024(en)
9.3.2 Larger test portion
9.3.2.1 General
A larger test portion is a sample that is larger than the test portion size that has been described in the
original method and/or validation document.
Testing a larger test portion can be necessary:
a) to reflect the microbiological quality of a large batch of product;
b) in cases where a large number of environmental samples is taken;
c) as sometimes required by national or regional legislation.
A larger test portion can originate from a single larger test portion (see 9.3.2.2) or from the pooling of
samples (see 9.3.2.3).
If a laboratory sample larger than the maximum sample size has been submitted, the sample can be split
into multiple test portions based on the maximum sample size (e.g. if a laboratory sample of 750 g has been
received for Salmonella testing it can be prepared as two 375 g test portions).
9.3.2.2 Larger single test portion
A larger single test portion is a sample that is larger than the test portion size that has been described in the
original method and/or validation document originating from a single sample. A larger single test portion
can be applied to both qualitative and quantitative testing.
9.3.2.3 Pooled sample
A pooled sample is a sample where a number of items have been combined and the complete mixture is
taken as a whole for examination in the laboratory. Items can be pooled:
a) out of the laboratory, where individual samples are combined into one larger pooled sample;
b) in the laboratory where individual test portions are combined into one larger (pre-)enrichment as
illustrated in Figure A.1;
c) in the laboratory, where individual (pre-)enriched test portions items are combined into one and carried
through as a single test as illustrated in Figure A.1.
A number of items may be pooled at the sampling stage by the client or laboratory (at the client’s request).
Pooling shall be applicable to qualitative tests only. Only items from the same origin or source (e.g. same
batch or lot) shall be pooled.
9.3.3. Procedure for larger test portion size
Items can be composited or pooled out of or in the laboratory as a test portion or as a (pre-)enriched test
portion but not as two or more combinations [i.e. pooling of (pre-)enriched as well as test portion is not
allowed].
To minimize the risk of false-negative results when testing a larger single test portion or pooled test portion,
proceed as follows:
— For qualitative analysis, the primary pre-enrichment broth shall be pre-warmed to the intended
incubation temperature with the same tolerance range.
— The temperature profile of the larger enrichment volume shall be checked to ensure that the time taken
to reach the target incubation temperature and overall incubation time are as specified in the individual
standard. For example, in ISO 6579-1:2017, 9.2, the pre-enrichment incubation time is between 16 h and
20 h. The temperature profile for the larger test portion size shall be between 34 °C and 38 °C with a
minimum incubation time of 16 h. The time needed to reach the target incubation temperature should
be minimized. Demonstrating compliance does not have to be for each individual sample but depends on
ISO 6887-1:2017/Amd.1:2024(en)
the temperature difference between the sample and the broth. Temperature profile shall be available for
frozen, refrigerated and room-temperature samples.
— When testing a larger single test portion, pooled test portion and pooled (pre-)enrichment test portion,
the dilution ratio (sample/diluent) used in the validated method shall remain the same as well as the
other incubation conditions (e.g. time and temperature). This ratio may be increased to overcome the
inhibitory effects coming from certain food materials as those mentioned in ISO 6887-4:2017, 9.1.4.4
(e.g. onion powder, garlic, oregano, peppers, certain teas and coffees, vitamin premixes, highly salted
products).
Additional pooling instructions may be described in individual standards (e.g. maximum sample size and
food category).
9.3.4 Validation and verification of larger test portion size
The larger test portion size can be used in other laboratories once this has been validated in a study in
accordance with ISO 16140-2 or ISO 16140-5. See the flow diagram in ISO 16140-4:2020, Figure 1. Once
validated in such a study, any laboratory can implement the larger test portion size after verification in
accordance with ISO 16140-3. For the verification of a larger test portion size, the same (food) category shall
be used. If not validated in accordance with ISO 16140-2 or ISO 16140-5, validation in accordance with the
protocol specified in ISO 16140-4:2020/Amd 1:2024, Annex H, is necessary for each laboratory wishing to
use a larger test portion size.
Qualitative reference methods which were validated using larger test portion size in accordance with
ISO 17468 and qualitative alternative (proprietary) methods which were validated using a larger test
portion size in accordance with ISO 16140-2 only need to be verified by a laboratory following ISO 16140-3.
Once the larger test portion size has been validated, all test portions smaller than the largest validated test
portion size can be used for routine testing for this particular (food) category at the same sample/diluent
ratio. For example, a method that has been validated for 375 g test portions can be used for 25 g, 100 g, etc.,
up to 375 g test portions.
Laboratories applying sample or test portion pooling that exceeds the maximum sample size stated in
the method shall carry out a validation using the protocol as specified in ISO 16140-4:2020/Amd 1:2024,
Annex H .
The relative level of detection (RLOD) approach specified in ISO 16140-4:2020, 6.1.1.3, shall be used to
demonstrate that a larger test portion size provides similar or lower level of detection (LOD ) compared
to the LOD of the (validated) test portion size as specified in the method. The corresponding protocol is
specified in ISO 16140-4:2020/Amd 1:2024, Annex H.
Annexes A, C and D
Replace each annex with the following text:
ISO 6887-1:2017/Amd.1:2024(en)
Annex A
(informative)
Compositing and pooling procedures
Figure A.1 illustrates the compositing and pooling procedures, which can be performed out or in the
laboratory.
NOTE 1 Numbers of items, mass of 25 g and 100 g, are used as examples. This mass may be changed.
NOTE 2 Reported results for both rows of compositing are
...