Reference materials for checking the performance of qualitative tests (presence/absence of pathogenic micro-organisms): properties, future needs, use in method validation

Abstract

Foodstuffs shall not contain pathogenic micro-organisms in concentrations which may cause a risk for consumer health. The relevant legislation therefore normally contains the requirement that these organisms are “absent” in a certain product quantity (e.g. 25 g). It is not at all easy to prove the “absence”. Reference materials are important tools for checking the performance of qualitative methods. These materials should contain the target organism in low numbers (close to 1 cell/capsule). Furthermore, the most important interfering micro-organisms should be taken into consideration, when testing the performance of detection methods using reference materials. When developing reference materials with the described characteristics, detection methods are needed which give a positive result with one or a few cell(s) of the target organism. While these requirements appear to be fairly obvious, precise statements on method performance are rarely available. Strategies to obtain this information are discussed. Further important aspects are practical considerations when using such reference materials for method evaluation. Statistical procedures can help to obtain the relevant information with a minimum of effort.