Resisting bacteria

Published on Tuesday, 04 September 2012 14:39
Written by Andrew Hook

Using state-of-the-art technology we have discovered a new class of polymers that are resistant to bacterial attachment. These new materials could lead to a significant reduction in hospital infections and medical device failures

Medical device associated infections can lead to systemic infections or device failure, costing the NHS £1bn a year. It has been estimated that 80% of the infections acquired in hospitals involve biofilms, surface associated bacterial communities within which bacteria show up to 1000 times higher resistance to antimicrobials and host defences when compared with their planktonic counterparts.

To reduce the incidence of device associated infections, new materials are required with resistance to bacterial attachment to prevent biofilm formation at the earliest possible stage. To achieve this we developed a high throughput materials discovery approach using a microarray format to assess the interaction of bacteria with hundreds of polymeric materials simultaneously. On a microarray, hundreds to thousands of materials can be expressed as small polymer spots on a single glass slide, allowing for the parallel assessment of material-bacteria interactions. Using this system, we assessed the attachment of three bacterial strains on nearly 500 unique materials in over 7000 separate assays (Pseudomonas aeruginosa, Staphylococcus aureus anduropathogenic Escherichia coli), a feat not possible using conventional techniques. In vitro we were able to reduce the numbers of bacteria by up to 96.7per cent compared with a commercially available silver containing catheter.

However, a key challenge for many biomaterials is to reproduce their in vitro performance within the in vivo environment where, in particular, protein adsorption can alter the properties of materials. To assess the performance of the hit materials in vivo, silicone catheters dip-coated with the hit polymer were implanted subcutaneously into mice and inoculated with S. aureus. After 1 day, we observed a >90 % reduction in bacterial numbers compared to a non-coated catheter, a difference that persisted for 4 days. By preventing bacterial attachment to the device, the body's own immune system was able kill the bacteria more effectively on our materials than the uncoated catheter where a biofilm was formed.

The materials resistant to bacterial attachment discovered in this study represent a new group of structurally related materials comprising ester and cyclic hydrophobic moieties that could not have been predicted from the current understanding of bacteria-surface interactions. These materials are ideally suited as coatings on medical devices such as urinary catheters, venous catheters, heart valves and stents to prevent device associated infections.

This is early stage research but the initial results are very promising. The next stage of this research will be to develop the manufacture of these coatings to enable the performance of these materials to be assessed clinically and we are currently in early stage discussions with a number of medical device companies. We believe that our hit materials will be ready for clinical use in 5 years time.

The research was led by Professor Morgan Alexander and Professor Martyn Davies in the School of Pharmacy and Professor Paul Williams in the School of Molecular Medical Sciences with the help of experts from the Massachusetts Institute of Technology (MIT). The results were published on Sunday 12 August 2012 in the prestigious academic journal Nature Biotechnology. This research was funded by a £1.3m four year Translation Award from the Wellcome Trust.

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