Atomic Force Microscopy of Biofilm Adhesion

The adhesive behaviour of extracellular polymeric substances to poly(ethylene terephthalate), a model hydrophobic surface, were measured in response to their degradation by enzymes known for their biofilm dispersion potential. By examining the physical changes in the nature of the binding, structural or adhesive roles could be established for the targets of the enzymes. Degradation of extracellular DNA (eDNA) significantly decreased the adhesive force of Micrococcus luteus biofilms with the surface, and furthermore almost completely eliminated any components of the biofilm maintaining the adhesion. This established a key structural role for eDNA.

Due to the significant results observed by the targeting of eDNA, a highly potent novel DNase was investigated to understand its mechanism of action. This would allow further optimisation of the enzyme to maximise its efficiency against a major structural component of bacterial biofilms. Rapid data collection and computer software was used to construct and validate a model of the enzyme activity. This resulted in real world conditions that must be met to maximise the activity of the enzyme, as well as providing direction for additional engineering of the enzyme's behaviour.

The tools and procedures developed during the study of the model bacterium, Micrococcus luteus, were used to study the adhesive properties of two pathogens, Leishmania mexicana and Staphylococcus aureus (S. aureus). Improving understanding of the adhesive mechanisms used by these pathogens allows for the development of new treatments against them. Custom MATLAB scripts enabled new data analysis of the interaction between Leishmania parasites and galactose-coated AFM tips. This helped elucidate the binding changes used by the parasite as it
matures and becomes infectious. Biofilm cantilevers were modified to examine a potential skin treatment that has the potential to decrease the adhesion of S. aureus to epithelial cells. A decrease in peak adhesion of 52 % was observed by force experiments between a biofilm-coated cantilever and treated human epithelial cells.