Certification by interlaboratory studies

In principle, the certification of RMs for microbiological parameters does not differ from the approach used by BCR for chemical parameters. They fall into the category of method-dependent CRMs certified for an activity. In fact, the microbes will behave differently from one type of method (in particular the culture medium) to another. For selective media the resuscitation rate of the microbes in the RM will change. Injured bacteria will have difficulties to form colonies on these media. This reflects the biological activity of the strain after stabilisation. As the method will strongly affect the result, it must be verified that the method was applied in a similar way by all participants. This means that accurate protocols have been prepared and tested beforehand in a feasibility study. The first step of the evaluation of the certification study will be to verify that the protocol was strictly followed. This protocol will be made available to the users of the CRM. 

Such certifications are only of interest if the method(s) used are recognised by the scientific community as reference methods. Therefore, BCR has certified its RMs through 

No major decrease in cfp per capsule could be noticed at -20 °C over 200 weeks. Y axis mean number of colony-forming particles of Salmonella typhimurium in one capsule (Ns,cfp). X axis weeks of storage at -20 °C. 

Compared to physics or chemistry, microbiology is not yet able to measure absolute parameters (non method-dependent). Therefore, concepts like accuracy or traceability 

---

Certification by interlaboratory studies using one or several different methods, possibly including definitive methods. 

---