Food testing laboratories serve as a critical line of defence between consumers and foodborne pathogens. A clear connection exists between quality testing and safety: the more robust the capabilities of food testing laboratories, the safer consumers can be.
To that end, the International Organization for Standardization (ISO) introduces standards that aim to ensure that these laboratories and the materials used are of the right quality. In terms of materials, this includes culture media for dilution, enrichment, enumeration, isolation and confirmation of micro-organisms.
EN ISO 11133 Microbiology of food, animal feed and water – preparation, production, storage and performance testing of culture media was developed with awareness of the global impact of ISO standards on consumer safety.
EN ISO’s publication of the update in 2014 substantially revised existing standards, replacing the technical specifications EN ISO 11133-1 and -2, and superseding ISO 9998:1991, and clarified previously discussed technical procedures.
The standard was compiled by committees focused on microbiological analysis of food products and water quality. It extensively defines the preparation and quality control of all formats of culture media related to food and water testing.
The guidance clearly delineates the requirements of both quality control laboratories and the manufacturers of culture media in maintaining compliance throughout the performance testing process. EN ISO 11133:2014 applies to all laboratories performing microbiological analyses of food for human consumption, animal feed, and samples from these products’ manufacturing environments, as well as to all kinds of water for consumption or use in food production.
The guidance covers dehydrated and ready-to-use culture media for classical microbiological methods, and media for alternative testing techniques. As such, it is necessary that all accredited laboratories performing microbiological testing of food, animal feed or water using culture media abide by the EN ISO standard.
Performance testing
EN ISO 11133 offers quality assurance management including practical guidance on media preparation in an exhaustive section; which discusses the water used for preparation, pH measurement and, if needed, adjustments, and storage of prepared plates, tubes, and bottles.
However, the main section of EN ISO 11133:2014 focuses on performance testing, providing guidance based on the principle that performance testing conditions should resemble the intended sample testing conditions as closely as possible in order to produce the most accurate and meaningful results.
Accordingly, culture media for quantitative testing must be tested quantitatively, and those used in conjunction with membrane filters must be tested with these filters. Culture media used for sample preparation and dilution are tested to keep the numbers of micro-organisms unaltered during the time of handling.
To that end, the guidance includes extensive detail on performance testing requirements and practical execution. Step-by-step instructions with flow charts are provided for executing and evaluating quantitative and qualitative performance tests.
The standard contains comprehensive tables for the specifications for most culture media, for both food and water microbiological analysis. These tables describe each medium’s target micro-organism, relevant ISO standard, and functions to be tested (productivity, selectivity, specificity), including the appropriate control strains for each function per their World Data Centre for Micro-organisms (WDCM) numbers, as well as test criteria and/or characteristic reactions.
EN ISO 11133 also contains hands-on, detailed instructions for the maintenance of microbial strains, as well as the preparation and standardisation of working cultures and inoculation suspensions. The standard specifies the optimal number of colony forming units (cfu) per plate or membrane filter, and describes how productivity ratios and limits are determined.
Who does what?
Laboratories increasingly source their culture media from suppliers to simplify their workflows and ensure high quality and consistency. EN ISO 11133:2014 stipulates requirements not only for laboratories that prepare their own media, but also for manufacturers.
With a clear line drawn between the quality assurance responsibilities of users and manufacturers, lab managers can now determine which duties and responsibilities no longer apply to them when they procure culture media.
For labs that produce their own culture media, it is usually sufficient to test each batch with a single test strain named in the standard, whereas manufacturers are expected to perform tests using several micro-organisms. However, both labs must meet the specified productivity and selectivity as described for each test organism.
Manufacturers need to conduct rigorous qualitative and/or quantitative testing for all EN ISO 11133-compliant culture media they provide. The end user’s responsibility upon receiving the media is to ensure that testing was performed according to the requirements of the standard.
The quality control certificate, which discloses the test organisms used, inoculation levels, acceptance criteria of the performance tests, as well as the test results, is provided by the manufacturer to the end user to fulfil the end user’s responsibility to ensure compliant testing.
Ready-to-use media allow laboratories to rely on the performance tests that the manufacturer conducts, as long as the transport conditions are in the specifications and the manufacturer’s performance test is strictly following the requirements of EN ISO 11133.
A pre-condition for outsourcing of quality control in this manner is that the supplier must have an appropriate quality system such as ISO 9001 in place. However, several countries are set to increase the stringency of their requirements for acceptable outsourcing.
These countries, including Germany, are requesting the superior ISO/IEC 17025 accreditation on ISO 11133 procedures from 2017 onward as a pre-requisite for outsourcing the performance testing. If a batch of culture medium is released by an ISO/IEC 17025-accredited manufacturer QC lab, it is granted that all requirements of EN ISO 11133 are followed.
The role of manufacturers
Manufacturers of culture media intended for food and/or water testing must abide by ISO 11133:2014, and some, including the QC labs at Merck, have taken the extra measure of securing ISO/IEC 17025 accreditation for both dehydrated and ready-to-use culture media subject to ISO 11133.
These media can be easily recognised by their new brand names: Granucult, ReadyPlate and ReadyTube.
ISO/IEC 17025:2005 is the worldwide quality standard for testing and calibration laboratories, and attaining this accreditation signifies full compliance of relevant culture media with EN ISO 11133 concerning the preparation, production, storage, and performance testing of the media, and as such allows for expedited approval of and confidence in test results.
Manufacturers can also support labs by providing as much relevant compliance documentation as possible, including the quality control certificate.
Merck supports regulatory compliance by providing end users with full EN ISO 11133 and other individual standard and regulation compliance documentation through the certificate of analysis and technical data sheet, and on the product label.
Finally, manufacturers can support laboratories as they undergo audits and inspections, pre-emptively by providing a high level of quality documentation, and on an ongoing basis as regulatory agencies ensure consumer safety through rigorous audits and inspections.
The authors
Dr Andreas Bubert, Senior Global Product Manager for Culture Media Food & Beverage and Barbara Gerten, Senior Scientist Traditional Microbiology, Merck Darmstadt, Germany
