Certified Microbiological Culture Materials

Although the work of ATCC and others has done much to ensure the reproducibility and even demonstrate some traceability of microbiological reference materials the development of microbiological Certified Reference Materials (CRMs), certified for number of viable life forms is seen as important for control analyses of water and food. Somewhat of a holy grail the development of such CRMs has long been hampered by the unstable concentration and insufficient homogeneity of viable organisms in the materials. 

This Section describes one of the first successful attempts, by a multi national project team funded by the European Commission s DC XII, to produce and certify a microbiological CRM that is both fit for purpose and meets the requirements of the ISO Guides. The first results are two bacterial strains, Enterococcus faecium (CRM 506) and Salmonella typhimurium (CRM 507) (fanning et al. 1995). Both are available as part of the EU BCR range of CRMs. 

Cultivation of bacterial strain Suspension in evaporated milk 

The homogeneity determination of the bacteria in the materials is performed by viable count followed by statistical evaluation of the cormts of sub-samples from the same capsule solution and of total counts of different capsules of one batch. An example for the homogeneity determination for a batch of capsules containing Enterococcus faecium is also presented in (Janning et al. 1995). 

After the performance of collaborative studies organized by the RIVM (National Institute of Ihiblic Health and Environmental Protection, Bilthoven, The Netherlands) and SM T certification studies were performed by a group of eleven or twelve qualified European laboratories. These examined simultaneously the materials using standardized methods following a very strict analytical protocol. Table 5.1 below shows data for CRM 506 (Mooijman et al. 1999)- 

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