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Introduction
Growth of bacterial biofilms in hygienic processing plant (for example, food or personal care) is a problem which can result in the bacterial contamination of the product. We are developing a software “toolkit” to facilitate the simulation of growth and biocidal control of biofilms in flow pipes. Such simulations could potentially be used to obtain insights into the hygienic control measures required in hygienic processing at low cost.
Bacteria, nutrient and biocide are modelled as random walk particles within a pipe with parameters to describe their interactions and concentrations. While this model is obviously a great simplification it does produce convincing biofilms and growth profiles.
The modelling of bacterial growth has been described by M H Zwietering, I Jongenburger, F M Rombouts and K van’t Riet (Applied and Environmental Microbiology, June 1990, p. 1875-1881).These authors statistically compared several sigmoidal functions containing biologically relevant parameters to describe a bacterial growth curve. They concluded that “the modified Gompertz equation was statistically sufficient to describe the growth data of Lactobacillus plantarum and was easy to use.” The modified Gompertz equation was given as:
![y = A exp [ -exp { (u_m e / A) (lambda - t) + 1 } ]](images/mod-gompertz.png "y = A exp [ -exp { (u_m e / A) (lambda - t) + 1 } ]")
where y = ln (N / N0), A = the plateau value of y, μm = the maximum specific growth rate and λ is a lag time. N is the number of bacteria which increase with time t from an initial inoculum N0 bacteria.
Work is continuing to refine the model further whilst retaining the computational simplicity of discretised particles. Below are some pictures produced by the toolkit.
Biofilm Simulation Results
Click on the images to view a larger version of the image.
