Studying the effect of High pressure processing on Listeria monocytogenes in food and developing a model to suppress its resistance.

High pressure processing (HPP) is a food treatment technique, developed to increase the shelf life of food by inhibition of microbial growth, at the same time as quality degradation is avoided. By using high pressure, the components in the food is less affected than by the use of many traditional preservation methods. However, the ability of bacteria cells to recover is an important concern in food safety. The lack of knowledge in this field may impair the use of HPP treatment as an efficient food preservation method, making it essential to understand these adaption responses. Since there is not enough experience with high pressure processing, more knowledge is needed on its specific features and on how this technique affects bacteria. In particular it is of interest to know how high pressure affects the bacteria Listeria monocytogenes as this is a food-borne pathogen which can cause severe illness to those who get infected by it. With the aim to learn more about the embedded mechanisms that allows bacteria to recover from pressure induced damages, a new strategy has been applied. This strategy includes the use of mathematical model simulations to get more insight in the behaviour and dynamics of cell recovery after HPP exposure. This approach includes three parts: 1. Creation of repair pathway models 2. Conduction of high pressure experiments 3. Simulating responses based on the experiments and developed models This thesis has showed the method of how simulations can be used to find out more about bacteria repair. Pressure induce leakages in the cell envelope are being repaired by activating repair mechanisms in the cell wall, cytoplasmic membrane and envelope associated proteins. The genes responsible for reparation are those involved in the synthesis and turnover of peptidoglycan, phospholipids and proteins as well as repair chaperones. From the experiments it was verified that high pressure induce leakages in the cell. Based on the results, it is suggested that L. monocytogenes requires approximately two days to recover, though this assumption needs more verification. The mathematical simulations showed that the repair system is particularly sensitive to degradation reactions, meaning that they have the potential to be target elements for reduction of bacteria resistance towards high pressure