Numerical modelling of the sticking process of a S. aureus bacterium

Abstract

The investigation of the dynamics of a single bacterium may help to understand the behaviour of a system of bacteria (e.g. biofilm formation) as well as the transmission of infections in the air. One of the important factors influencing the stability of a bacterial structure but also important in the context of an infection is the adhesion force. In order to model the sticking process over time, two theoretical models for bacteria are presented. These models allow to simulate the sticking process numerically. As the model complexity, may affect the calculation time, in this paper we derive two theoretical models of different complexity. One is a simple, adhesive viscous elastic, the other a more complex adhesive viscous elastic-plastic model. Both models can be applied to the simulation of the dynamics of bacteria. Thereby forces act when the bacterium is at a distance to a surface as well as during its contact. The attractive force is described by the van der Waals force by applying an adhesivedissipative model. For the description of the bacterium within a liquid medium electrostatic double-layer and steric force models are additionally considered. In the attractive-dissipative sticking process viscous damping forces were considered, which results in the theoretically expected load-unload behaviour. The sticking process of a bacterium on a substrate is solved by applying the discrete element method. The bacterium addressed is S. aureus; while as substrate glass is considered. The parameters needed for the numerical simulation of this bacterium are taken from published physical experiments performed with atomic force measurements. Detailed results on the sticking process of the bacterium are presented. A characterisation of the influence of repulsive and attractive forces on the bacterium is given. Obtained results are shown in terms of force displacement diagrams as well as a function of the sticking time history.