On-line Quantification of Thickness and Strength of Single and Mixed Species Biofilm Grown Under Controlled Laminar Flow Conditions

This study describes cleaning investigations of biofilms comprised of Escherichia coli and Burkholderia cepacia grown on polyethylene, stainless steel and glass substrates. Their adherence behaviour was determined under controlled hydrodynamic conditions using the non-contact technique of Fluid Dynamic Gauging (FDG). FDG utilises flow data to estimate (i) the adhesive (between biofilm and substrate)/cohesive (between cells and extracellular polymeric substances) strengths, and (ii) the thicknesses of biofilms. The thickness of single and mixed species biofilms increased linearly with time and plateaued at 14 days with no significant reduction thereafter. The asymptotic thickness of mixed species biofilm were thinner than E. coli biofilms. The adhesive strength, on the other hand, peaked at approximately 14 days with a significant reduction thereafter. The results showed that the development of biofilm thickness and attachment strength are not affected by the range of surface roughness and surface energy employed. However, the increase in strength is strongly correlated to the protein and glucose content of the biofilms. Confocal laser scanning microscopy results confirmed an increase in the percentage of dead cells after 21 days, contributing to the weakening of the biofilms. Interrupting the flow of media during biofilm development had a negligible impact upon the thickness, but was found to significantly increase the biofilm strength.