Numerical modeling of bacterium-surface interaction by applying DEM

Abstract

In order to understand the behaviour system of the bacteria it is important understand the behaviour of a single bacteria. The suspension forming bacteria may be considered as system of living active ultrafine particles (size 1 μm). Present investigation addresses to the simulation of the S. aureus bacterium-surface interactions in a framework of the Discrete Element Method (DEM). Bacterium is of the spherical shape, while the glass surface is flat and considered as elastic. In this work the theoretical model for bacteria is similar to that used for the ultrafine size stiff particles. We investigate the behaviour of the active particle by applying two known Derjaguin, Müller, Toporov (DMT) [1] and Derjaguin, Landau, Verwey, Overbeek (DLVO) [2, 3] models, which are used for simulation of ultrafine size objects. These models are enhanced by applying suggested dissipation mechanism related to the adhesion. It was assumed that energy can be dissipated and the force-displacement hysteresis can occur through the adhesion effect, where an amount of dissipated energy is fixed and independent on initial kinetic energy. This force-displacement hysteresis was observed at the physical experiments with bacteria provided by the means of the atomic force microscopy (AFM), Ubbink and Schär-Zammaretti (2007) [4]. It was illustrated that the presented adhesive-dissipative model, which applies DEM, offers the opportunity to capture dissipation effect during the contact. The numerical experiments confirm that forcedisplacement plots exhibit hysteresis typical to those which are observed in AFM experiments. This model can be useful for numerical simulation of interaction of bacterium to the substrate.