Listeria monocytogenes is a gram-positive bacterium, which can cause listeriosis, a serious disease with high mortality in immunocompromised individuals, unborn children, and neonates. Listeria monocytogenes is able to grow at temperatures as low as –0.4°C and survives mild preservation treatments. These features make this bacterium a difficult but very important target organism to be eliminated from the food chain. A problem observed in minimal processing is that a small portion of a bacterial population can be relatively resistant. This phenomenon is called ‘tailing’, and it is of great importance for the food industry because of its possible implications to the food safety and the design of a process.
Aim: The objective is to explain the origin of the phenomenon ‘tailing’ for certain food pathogens in minimal processing and to translate this into a controlled design for industrial processing.
Research: Several strains of Listeria monocytogenes will be tested for their ability to produce subpopulations which are more stress resistant and will cause tailing under different stress conditions (high hydrostatic pressure, heat). These subpopulations will be further characterized, to identify the origin of this tailing phenomenon. Therefore some questions have to be answered: Is tailing dependent on the type of inactivation? How often does tailing occur in different strains and species? What is the basis of increased stress tolerance of subpopulations? And what can be said about prediction and prevention of tailing?
PhD-fellow: Ir. K.H. Van Boeijen, MSc (Ineke)
Supervisors: Prof. Dr Ir. M.H. Zwietering (Food Microbiology, WU), Prof. Dr T. Abee (Food Microbiology, WU), Dr R. Moezelaar (Agrotechnology & Food Innovations, WU)
Project term: July 2004 – July 2008
Sponsors: WCFS