A Kinetic Model for Bactericidal Action in Biofilms

Abstract

The standard methods for the determination of biocidal activity measure the rate of planktonic and/or sessile cell death. The role of diffusion within the biofilm on the kinetics of sessile cell death is generally not considered. It is known that, in the majority of cases, sessile cells are more resistant to biocides than are planktonic cells. The reasons for this increased resistance have been considered to be altered cell physiology or failure of the biocide to penetrate the biofilm. A model is presented which demonstrates how the rate of diffusion of biocides through a biofilm influences the rate of cell death. The calculations may be performed using a simple spreadsheet package. The results show a biofilm will decrease the rate of cell death even when microbial physiology in the biofilm is unaltered. Using this model, the increase in biocide concentration required to kill sessile, rather than planktonic, cells in the same physiological state in a given time may be estimated. The effects of altered cell metabolism may be considered only once the effect of diffusional time lag on the rate of cell death within the biofilm is known.