Quality assurance and standardisation

To improve the quality of the microbiologieal analysis of food and water most attention has been directed towards the formulation of standardised methods and the development of criteria for culture media, critical reagents, membrane filters and the essential basic materials. 

Internationally, standardisation of methods has mainly been carried out within the framework of the International Organisation for Standardisation (ISO) although other organisations such as the Comite Europeen de Normalisation (CEN) or the International Dairy Federation (IDF) for dairy products are also actively involved. The choice to standardise a method is not always sufficiently based on comparison of methods or on performance characteristics. Acceptance of international standard methods takes considerable time as all countries or states involved have to agree on the proposed method. Despite the availability of a great number of internationally accepted methods there are still important differences between the national methods used in EC member states. There are namely situations for which a national method is optimised for a local 

The use of different laboratories can give rise to results that are not comparable. Van Schothorst et al. [31] showed that despite the use of a carefully described standard method for the isolation of Salmonella from minced meat, the results from all laboratories were not the same. Differences between laboratories became especially apparent when samples were used with an even distribution of low numbers of Salmonella and high numbers of competitive flora. In this latter case four laboratories examined 100 artificially contaminated samples. The total number of samples found to be positive for Salmonella varied from 43 to 93. The differences were attributed to laboratory-associated factors such as differences in incubators, media preparation, time available to carry out the work, interruptions etc. When the analysis was carried out by the same workers, but in a single laboratory (repeatability), there were small (not significant) differences in the results. These differences were much smaller than when the analyses were carried out in different laboratories (reproducibility). The small differences were ascribed to the so-called human factor, that is interest, skill, dexterity etc. 

Within the EC, existing and proposed Directives have implications for food and water microbiology laboratories with respect to standardisation methods and laboratory accreditation if there is to be mutual recognition of results within the single market. It is therefore important to be able to check both the performance of a method (national or international) as well as that of individual workers. The reference materials which have been and which will be developed and hopefully certified, will thus be available for the verification of both types of performance. 

---