Individual-based modelling of growth and migration of Salmonella enteritidis in hens' eggs

An individual-based model (IbM) was developed to describe the growth and migration of Salmonella enteritidis in hens' eggs. The Bacteria Simulator (BacSim) environment was used to implement the model; the bacteria are represented by spheres that grow by nutrient uptake and divide in two daughter cells upon exceeding a certain threshold volume. Motility of the Salmonella bacteria was described by a run and tumble mechanism. For the sake of simplicity, the bacteria were assumed to grow exponentially, an appropriate assumption for the initial phase of growth relevant for shelf-life predictions. Both albumen and yolk were assumed to be homogeneous. The impact of several model parameters (chemotaxis, growth rate, initial contamination numbers and bacterial swimming speed) was assessed by a sensitivity analysis. The results show that chemotaxis towards the yolk would have a strong effect on the time needed to reach the vitelline membrane, an aspect that future research should focus on. The contamination position had less impact on the time to reach the vitelline membrane. The simulation results illustrate the need for more detailed knowledge on the subject of bacterial migration in hens' eggs. Our model can easily incorporate this knowledge when it becomes available.