In detection tests, the enrichment broth is typically inoculated with a predetermined concentration of the target organism sourced from the Certified Reference Material (CRM). This spiked sample undergoes the complete analytical process, it simultaneously checks the enrichment broth and the incubator, a PCR step or any other rapid method, if used, and selective agars. The certified reference material is accompanied by a certificate containing crucial information regarding its composition.

An example of the level of target organisms from a certificate:

 

The quantity in this certificate is given in CFU/g. If you intend to verify the method for detecting Salmonella spp., follow these steps: Accurately weigh the material (10 grams) and add diluent in buffered peptone water. While the standard procedure involves a 1/10 dilution, you can adjust the dilution ratio to suit your specific requirements. The expected level (assigned value) according to this certificate is 2700 CFU/g of Salmonella spp., with a range spanning from 1100 to 4900 CFU/g. If diluted at a 1/10 ratio, the expected level becomes 270 CFU/ml with a range of 110 to 490 CFU/ml. By inoculating your control sample with 100 µl of this solution, you will have an approximate level of 27 CFU. Adjust the level as necessary and adhere to your standard procedure. Inoculate the enrichment broth that fits your target organism. The same primary dilution may be used for both L. monocytogenes and Salmonella spp.

In summary: Check the certificate’s expiry date. Review the expected level and tolerance limits. Determine the desired inoculation level and adjust the dilution accordingly.

The material can also be used to spike a chosen matrix. This is beneficial for validating/verifying a new method or verifying an existing one. Alternatively, it can be used alongside the analysis of a customer's sample. This proves especially valuable when the sample material is unfamiliar to the laboratory or where, for some reason, there is uncertainty whether the target organism can be recovered from the particular matrix. In this process, one of the customer's samples undergoes standard analysis, while the other is spiked with the desired level of CRM. Both analyses are carried out simultaneously. This approach ensures a potential recovery of the target organism from this specific material, accounting for its inherent properties and natural flora. Unknown sample materials may contain competing flora and/or unidentified inhibitory substances, and spiking provides insights into these factors. 

CRM Certificates

Understanding key points is essential for effective usage of the CRM certificates.

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