Materials Analysis of Bacterial Adhesion and Early-Stage Biofilm Development

Bacterial adhesion and the subsequent biofilm formation is a complex phenomenon which has many consequences in water filtration. This aggregation of microorganisms can be difficult to remove from nanofiltration and reverse osmosis membrane surfaces, causing damage and eventual replacement of the membrane. In order to elucidate the cause of this biofilm formation, three influential factors were studied: surface topography, nutrient concentration and shear stress. Analysis was performed on the surface topographical heterogeneities in order to examine the influence of surface topography. Image analysis of the adhesion of Pseudomonas fluorescens (Ps. fluorescens) and Staphylococcus epidermidis (S. epidermidis) to the surface topographical heterogeneities was determined for two commercial membranes, NF270 and BW30, using a flow-cell system. Membrane area analysis, using AFM and SEM, showed up to 13% of topographical heterogeneities on the membrane surface with up to 30% of total adhered cells that were discovered within these topographical heterogeneities. For the analysis of the nutrient availability and shear stress on the structural formation of Ps. fluorescens biofilm under two different dynamic conditions, an air-liquid interface biofilm and a flow cell grown biofilm were assessed by confocal scanning laser microscopy (CLSM). The analysis showed a three-fold increase in the EPS biovolume of the high nutrient air-liquid interface grown biofilm. However, the flow cell biofilm increased the biovolume for low nutrient and higher shear stress conditions, suggesting harsher growth conditions of the biofilm results in greater biofilm development. Finally, the adhesive and viscoelastic properties of the Ps. fluorescens air-interface grown biofilm for two different nutrient dilution factors was determined by nanoindentation. The low nutrient availability showed higher adhesion force and work of adhesion with distributed colonies across the surface, while the high nutrient grown biofilm led to a reduction in the adhesive and elastic nature of the biofilm.