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Living Patchy Colloids

Final Report Summary - LIVPAC (Living Patchy Colloids)

Bacteria are proficient at colonising both naturally occurring and man-made surfaces. This colonisation often starts with the adhesion of just a few cells. Once attached to the surface, cells can assemble into a biofilm, a large agglomeration of cells embedded in a supporting matrix which protects them from both chemical and physical threats. Biofilm formation on medical equipment, implant organs, food packaging, and water distribution systems presents major healthcare and economic challenges. The main goal of this project was to study interactions of bacteria with surfaces, and to characterise the initial adhesion. This work has the potential to guide the design of novel antimicrobial coatings.

Within the project, we have studied the adhesion of rod-shaped Escherichia coli (E. coli) bacteria to treated glass surfaces by recording thousands of high-resolution videos. We have developed high-throughput tracking algorithms to process these videos and characterise bacterial motion on the surface. We used the extracted dynamics to automatically distinguish between cells that are either freely moving on, or adhering to the surface. We also investigated the motion of the cells after they had adhered to the surface.

We quantified bacterial adhesion to different surfaces and studied how the adhesion of E. coli to glass surfaces can be inhibited by chemical treatment, i.e. the addition of a non-ionic surfactant. One important finding of our work is that even within a population of genetically identical bacteria there can be large differences between individual cells in their ability to adhere to surfaces. Some cells directly adhere upon making contact with the surface, while others remain in solution indefinitely. Among the adhering cells, there are further distinctions - some cells adhere only weakly and freely rotate on the surface, while others are firmly bound with no rotational motion. These results can be explained with a simple model where each cell has a different number of adhesive patches on the surface. The differences in sticking ability are related to variations in the number of these patches. Our results suggest that diversification in adhesion properties could play an integral role in bacterial survival, which should be considered when designing anti-microbial surfaces.

We have also studied interactions of bacteria with synthetic micron-sized colloidal spheres on a surface, both experimentally and with computer simulations. In particular, we characterised the role of hydrodynamic and steric interactions, finding that these have strong effects on the bacterial dynamics.

The main results of this project have been presented at international conferences and published in peer-reviewed scientific journals, or are scheduled to be published in the near future. This project has also initiated and catalysed a number of collaborations in related areas, such as the swimming dynamics of bacteria, the behaviour of bacteria in complex emulsions, and simulations and experiments on anisotropic patchy colloids. Results from the project have also been presented at public outreach events through video and live demonstrations.

The work performed in this project has potential for direct application to the control of microbial adhesion. The results will be particularly relevant to the design and testing of new coating materials, e.g. for medical equipment, food packaging, and marine applications. We are currently performing a case study that builds on results from this project to investigate the adhesion of microbes to surface coatings for ship hulls.

Updates will appear on the project website.