Using a novel AFM methodology for biofilm cohesive energy determination

Biofilms can be undesired, as in biofilms covering medical implants, and encouraged, such as when they are used for waste treatment. We must understand both the growth and detachment stages of biofilm development if we hope to better remove or encourage the growth of these films. Whereas factors responsible for biofilm growth are well studied, those controlling the detachment process are not clearly understood. Understanding the cohesive interactions in the biofilm matrix could lead to the design of new strategies for controlling biofilm development. In this study we used AFM to develop a method to reproducibly measure, in situ, the frictional force on moist biofilms during tribological wear via a raster-scanned tip under elevated loads. The volume of biofilm displaced and the corresponding frictional energy dissipation were determined as function of biofilm depth and the cohesive energy density calculated. We found that the cohesive energy density was ~20 times higher at the cell surface compared to material, likely extracellular polymeric substances (EPS), surrounding the cells. Ongoing experiments in our laboratory are focused on applying this method to study the cohesive energy density of biofilms grown under different conditions. This method could also be used to investigate biofilms subjected to treatment with different biocides in order to determine how best to remove them