Case study n°3 & n°4

Bacillus cereus in REPFED

Bacillus cereus is a common micro-organism, occurring in soil, air, dust, water and in many raw and processed food. It is able to survive different environmental stresses and is causing major problems for food industry. B. cereus can be transmitted to food products when contaminated ingredients are used. It is found in a wide variety of food. Milk and milk products are among the main foods of concern with respect to the B. cereus problem. Milk is already infected at the farm and pasteurization kills vegetative bacteria but the spores survive and are activated by pasteurization. B. cereus spore are commonly isolated from dried foods, for example from spices and consequently spiced dishes are contaminated. Rice is also frequently contaminated with B. cereus and the presence of this bacterium in rice can lead to food poisoning if boiled rice is stored at abusive temperature during cooling. Because B. cereus is ubiquitous in nature, a lot of other foods are contaminated with pathogen such as meats, vegetables, cornstarch, cereals, etc.   
Bacillus cereus is then a food borne disease agent which constitutes a major concern for food processing industries, particularly industries which produce refrigerated processed foods of extended durability (REPFED). Indeed, the pathogen produces heat resistant spores and some strains can grow at temperatures of refrigeration (psychrotrophy). Moreover, it is a frequent cause of permanent contamination of REPFED because B. cereus persists on the surface of food processing equipment due to the high adhesion of its spores and its ability to form biofilms. It is therefore a hazard for foods treaded on line in continuous processing.
Based on two in-progress projects, we aim in this project at linking the HACCP measures in the REPFED’s industries to the modelling of the risk of emergence of B. cereus in these industries. As an example for the vegetable puree, the QRA model, which is being built, and which includes the industrial part in detail, will be the starting point to link the HACCP criteria to the impacts of various elements in the industrial pathways in terms of their contribution to the overall risk to human health. The aim of the project is thus to establish industrial control measures based on a QRA model for a very persistent pathogen in premises and equipment. Furthermore, the B. cereus family is large and the characteristics of the strains are heterogeneous as regards adhesion, biofilm, heat resistance, psychrotrophy and virulence.

Listeria monocytogenes and Staphylococcus aureus in dairy products

L. monocytogenes has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in processed foods such as pâtés, hot dogs, deli cold cuts and soft cheeses (feta, brie, camembert, Mexican or blue-veined). Unpasteurized (raw) milk or foods made from unpasteurized milk may contain L. monocytogenes. Although pasteurization is sufficient to kill the bacterium, contamination can occur after processing. Quantitative risk assessment models of human listeriosis linked to consumption of soft cheese made from raw milk were conducted (Bemrah, 1998, Sanaa, 2004). The models assessed the prevalence and concentration of Listeria monocytogenes in cheeses throughout the various steps of production from farm to table. Only contamination arising from the raw milk was taken into account. It was assumed that for the type of cheese studied, white-rind soft cheeses made with raw milk (camembert and brie de Meaux), the impact of cross-contamination was negligible when good hygienic practices and HACCP were observed. Pasteurized milk is more concerned with cross-contamination since contamination of the product surface can occur during both processing and ripening. Operations such as smearing of cheese surfaces increase the risk of undesirable microorganisms being present on the product surfaces. Taking such operations into account would significantly modify the results of any QRA of pathogens in such cheeses made with raw or pasteurized milk. A comprehensive model including cross contamination is now available (Aziza, 2006). This model will be applied to one type of soft cheese made with pasteurized milk. This application will be used to demonstrate the usefulness of QRA on optimising HACCP measures and on defining the critical limits and monitoring sampling frame.
Staphylococcus aureus in a traditional semi-hard cheese made with raw milk will be modelled. This example will demonstrate how to manage the presence of the hazard at different steps of the production and the possible production of enterotoxins. The establishment of efficient HACCP measures is crucial to maintain this type of traditional products. The HACCP measures should remain compatible with the economic viability of such productions.