Ask the Sample Prep Expert: Certified Reference Materials

The increasing adoption of ISO/IEC 17025:2005 accreditation for food testing laboratories has created a need for certified reference materials for validating quality assurance and product safety. This includes the use of microbial certified reference materials produced under ISO guide 34 conditions when available or, when not available, the use of a reference strain from a recognized culture collection.

What is a Certified Reference Material (CRM) in microbiology?
In general, a CRM is a high-quality standard, where at least one value is certified according to ISO/IEC 17025. In microbiology, CRMs refer to microorganisms used as test strains to confirm the quality of media and test methods used. These certified reference materials must be produced under reproducible conditions compliant with the ISO guide 34 (General requirements for the competence of reference material producers) and then certified according ISO/IEC 17025. Vitroids™ and LENTICULE® discs are examples of CRMs containing viable microorganisms in a certified quantity produced ISO Guide 34:2009 using authenticated strains from NCTC, NCPF, ATCC and other strains. Consisting of pure cultures of bacteria or fungi in a solid water soluble matrix, they are stable for at least one year and are in a viable state with a shelf life of 1-3 years. The within batch variation for every product is very low. In some cases, the standard deviation is less than 4 colony forming unit (CFU) at the level of 100 cfu. Each batch is provided with a comprehensive certificate of analysis that specifies the mean number of colony forming units, an expanded uncertainty about the mean, details about the method used to determine the product data and the number of passages (subcultures) from the original strain.

Is it possible to use Certified Reference Materials (CRMs) to test the performance of media acc. ISO 11133:2014?
The new ISO 11133 is a norm describing the preparation, production, storage and performance testing of culture media. This norm states that the needed working culture can be prepared from a commercial reference material (RM or CRM) or by the laboratory. The protocol describes the use of reference materials (RMs), CRMs or internally produced RMs for determining the recovery rate of media. For example, Vitroids™ and LENTICULE® discs provide a stable bacterial suspension containing a known number of colony-forming units of the target or unwanted strain. The recovery from the new batch of culture medium will be compared to the expected number of CFU from the CRM. With a CRM, the value is more reproducible and saves a lot of time as it is already prepared and easy to handle.