The Physics of Bacteriophage-coated Antimicrobial Surfaces

Bacteriophages (phages) are viruses that prey on bacteria. In the early 20th century they were widely used to treat dangerous bacterial infections, e.g., cholera, but their popularity was eclipsed by the rise of conventional molecular antibiotics like penicillin. However, the growth of antimicrobial resistance (the rapid evolution in bacteria of resistance to conventional antibiotics) is now driving a resurgence of interest in phages as effective antibacterial agents, with approximately 40 phage-based companies set up so far worldwide. Many of the antibacterial applications rely on binding phages to surfaces, e.g., food packaging, seed coatings, animal feed, catheters and wound dressings, and companies, including the project partner Fixed Phage Ltd, are actively researching how to do this in a way that retains maximum antibacterial activity. The aim of this proposal is to understand the basic science underlying this problem, and to apply this understanding to design and optimize these phage-coated surfaces.

For human infections, we have the benefit of detailed mathematical models that help us to stop these infections spreading. I want to be able to use these mathematical models to enhance the spreading of phage infections among bacteria, but there are several basic science questions that must be answered before this can be done. This proposal addresses three of these questions, which are also of direct relevance to understanding how bacteriophage-coated surfaces work:

1) How does phage infection affect bacterial swimming and vice versa? Many bacteria swim, and this can spread the phage infection further. This is analogous to the way human infections can be spread by long-distance air travel, but for bacteria, very little is known; even the simple question of whether bacteria stop swimming immediately after infection, or just before they die some minutes later, remains open. Understanding this difference is important for mathematically modeling phage infections, including on antibacterial surfaces, and will help to determine important design parameters such as the density of phage coverage needed to ensure the infection spreads through the whole bacterial population.

2) How are the phages distributed and oriented on the surface? Phages inject DNA into bacteria through tube-like tail fibres. To be effective these fibres must contact the bacteria, but phages probably bind in random orientations, which will limit their activity. Similarly, the most effective phage-coated surfaces will have a uniform distribution of phages across the surface, but a widespread phenomenon in drying droplets, called the 'coffee-ring effect' may cause the bacteriophages to clump together. This is particularly significant because bacteria attached to surfaces can grow and aggregate into highly resistant colonies known as biofilms; a phage-poor region of the surface presents an ideal opportunity to do this. This leads to:

3) How does bacterial aggregation affect infection dynamics? Dense bacterial aggregates present a physical challenge for bacteriophage treatment (the phages can't get in), but they can also act as phage reservoirs. Understanding the competitive dynamics between bacterial aggregation and phage infection is a key challenge, and modelling this will be important for a wide range of applications. This includes using phages to treat human infections, where resistant biofilms pose a huge challenge.

I will address these questions with experiments and mathematical modelling, looking for fundamental physical principles that can be applied to optimize antimicrobial surfaces, and design new devices for novel applications. With the aim of developing clinical applications, I will also test how these principles carry over into a system containing bacteriophages, bacteria and cultured human cells, which is a model for bacterial infections.

Industrial Impact - The main industrial beneficiaries of this work will be companies that exploit bacteriophage technologies for antibacterial applications, principally my industrial partner Fixed Phage. Bacteriophage-based technologies are one strand of attack in our battle against antimicrobial resistance (AMR), which is a global challenge with huge social and economic implications (see Review on Antimicrobial Resistance. Antimicrobial Resistance: Tackling a crisis for the Health and Wealth of Nations. 2014). Basic science knowledge about how bacteriophages and bacteria interact on surfaces like food packaging or catheters will assist in optimizing existing bacteriophage-based technology, and developing it for novel applications. With Fixed Phage I also expect to adapt the techniques and models developed through this research to serve as quality control and research and development tools, e.g., to determine the distribution of bacteriophages through a phage coating.

Training - The simultaneous challenges (or opportunities) of AMR and the 'big data' revolution call for a new generation of researchers skilled in both microbiology and physical sciences, with the ability to look beyond academia and envisage or exploit the practical implications of their research. This combination of skills is rare, and this research proposal will help to meet this need.
From Fixed Phage the Edinburgh PDRA and PhD student, as well as other undergraduate and graduate students associated with the project, will receive comprehensive training in phage and microbiology research in a rigorous industrial environment; this insight into industry will also give these researchers a stepping stone to forging their own industrial links later in their career.

Scientific Impact Across Disciplines - This work will reveal the basic science underlying bacteriophage-bacterial interactions in complex model environments. The immediate beneficiaries will be phage biologists, microbiologists, and biophysicists. The work on drying bacteriophage droplets will also contribute to general research into the drying of other complex droplets, e.g., blood drying for forensic science applications, or pesticides on crops.

Outreach - I will run 3 workshops on bacteriophages at venues such as the Edinburgh Science Festival. These workshops will introduce bacteriophages to the general public as objects of scientific and general interest, helping to overcome some of the barriers in public perception of phages, associated with viruses and genetic modification.