Microbiological reference values for foods: a European perspective

Microbiological criteria for food products and meals serve to gauge the results obtained upon monitoring samples from manufacturing plants or catering units which strictly adhere to good manufacturing practices (GMP). Hazardous practices thus already having been eliminated, the aim of monitoring is to detect and, above all, immediately correct accidental failures in processing or preparation. An essential element of this system of monitoring is that the number of criteria used is kept to a minimum by carefully selecting the criteria of major ecological significance. In view of the sporadic and erratic distribution of pathogenic organisms in foods from well-run manufacturing plants and food service operations, criteria for disease agents are used only occasionally. Where they are used, their selection and detection methodology require intensive and expert scrutiny, including (i) careful designation and precise definition of the relevant agents of disease, toxin formers, or preformed toxins; (ii) prescription of very carefully validated and standardized methods, usually including a resuscitation step; and (iii) mathematically correct interpretation of failure to detect particular infectious or toxinogenic organisms. On the other hand, "marker" organisms ("indicator" and "index" organisms, according to Ingram) are frequently used. These should also be carefully selected by ecological surveys on each specific food product; in particular, their value for reliably revealing deficiencies in hygiene or handling should be assessed. The applicability of the entire group of Enterobacteriaceae (or particular parts of that taxon), Enterococcus species, Staphylococcus aureus, and streptococci of the "mitis-salivarius" group are critically examined. Numerical reference values for microbiological criteria are derived by mathematical treatment from data obtained in surveys of products produced under GMP previously validated by safety analysis. Target values thus derived will include tolerance limits and policies recommended in case high results are obtained. Consequently, "3-class sampling plans" (according to ICMSF) are to be used in most instances.