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The certification of a reference material for the evaluation of the ISO method for the detection of Salmonella
P H in 't Veld1, N G van Strijp-Lockefeer, A H Havelaar
1Laboratory of Water and Food Microbiology, National Institute of Public Health and the Environment, Bilthoven, The Netherlands.
Abstract:
A reference material (RM) containing Salmonella typhimurium was certified as CRM 507 by the Standards, Measurements and Testing Programme of the European Commission. The material consists of a gelatin capsule filled with artificially contaminated milk powder. The material is certified for the evaluation of presence/absence methods based on the ISO 6579 procedure for the detection of Salmonella. In the certification study 11 laboratories determined the presence/absence of Salmonella from each of 50 capsules. They also determined the mean number of colony-forming particles (cfp) and the homogeneity of the batch of RM according to an enumeration procedure. Certified values were calculated for both procedures separately. Based on the presence/absence procedure a fraction of capsules in which no Salmonella could be detected of 2.7% (one-sided 95% confidence upper limit 4.4%) was certified, for the enumeration procedure this fraction was 0.61% (one-sided 95% confidence upper limit 1.6%). The certified mean number of Salmonella cfp in one capsule is 5.9 (two-sided 95% confidence interval 5.3-6.4). Data on the preparation, identification, stability (at storage and higher temperatures) and homogeneity of the material are presented.