Food Microbiology

BIPEA organizes regular proficiency testing schemes (PTS) in many analytical domains, including microbiology in food. In order to help laboratories with their regulatory requirements issues, BIPEA developed a production of external reference materials (ERM) for microbiology in food. These samples should allow laboratories to check the trueness of their results at any time, outside the regular P-tests. For that purpose, BIPEA produced stable and homogeneous samples of meat contaminated with Escherichia coli, Clostridium perfringens, Bacillus cereus, Staphylococcus aureus and Listeria monocytogenes, at levels between 102 to 104 colony forming unity per gram (CFU/g). To check the production, controls were performed by analysing some samples all along the production process at the beginning of the study and at regular intervals during a 6 month period. The homogeneity was checked by calculating coefficients of variation, which were inferior to 30% for all the analytical parameters. The stability was characterized by comparing means of three samples to the mean obtained at the beginning of the study. The samples produced were thus considered as being sufficiently homogeneous and stable to meet the requirements of ERM: the results of enumeration of the different micro-organisms present in the minced meat after 6 months of storage at (-24±6) °C showed a good stability, with a maximum deviation inferior to 0.5 log (CFU/g).