In natural and manmade environments, bacterial biofilms are ubiquitous, yet the significance of biofilm contamination in a clinical setting is often underestimated [1]. Such contamination presents a particularly virulent form of infection that is shielded from systemic antibiotics, providing ideal conditions for the emergence of multidrug-resistant colonies [2]. There is an unprecedented need to establish new strategies to manage the colonization of clinical surfaces with these complex bacterial communities. This contribution explores the use of cold atmospheric pressure air plasma for the inactivation of clinically relevant biofilms grown on medical grade titanium. Furthermore, the impact of the plasma treatment on the properties of the host surface is investigated.

Using a 1D air plasma model [3], supported by experimental measurements, the chemistry of a Surface Barrier Discharge (SBD) suitable for biofilm inactivation was shown to contain a wealth of long-lived species such as O₃, NO₂ and N₂O. Under the influence of a convective flow, the presence of species that are traditionally considered to be too short-lived to reach a downstream sample are predicted, e.g. OH. [4]

The SBD system, shown in Figure 1, was found to be highly effective for the decontamination of single and mixed species biofilms, achieving a multiple log reduction within 60 seconds of exposure. Given that the surface composition and morphology are key factors influencing biofilm formation, the impact of the plasma decontamination process on the surface characteristics was assessed and shown to induce considerable changes. The impact of these changes on the ability of bacteria to adhere to plasma treated titanium surfaces was examined. It was shown that biofilm formation on surfaces subjected to the plasma treatment was found to be accelerated in comparison to untreated surfaces.

This study demonstrates that cold air plasma is an effective tool for biofilm elimination on clinically relevant surfaces, yet the choice of plasma system must be carefully considered as such treatments can significantly alter the ability of bacteria to attach to the surface.

[1] D. Lindsay, A. von Holy, Journal of Hospital Infection. 64, (2006), 313-25.

[2] J. Davies, D. Davies, Microbiol Mol Biol Rev. 74, (2010) 417.

[3] M. Hasan, J. L. Walsh, J. Appl. Phys. 119, (2016), 203302.

[4] M. Hasan, J. L. Walsh, Appl. Phys. Lett. 110, (2017), 134102.

[5] Y. Ni, Y., M.J. Lynch, M. Modic, R.D. Whalley, J.L. Walsh. Journal of Physics D: Applied Physics, 49 (35), 355203 (2016).