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The antimicrobial activity of atmospheric pressure non-thermal plasma has been exhaustively characterised, however elucidation of the interactions between biomolecules produced and utilised by bacteria and short plasma exposures are required for optimisation and clinical translation of cold plasma technology. This study characterizes the effects of non-thermal plasma exposure on acyl homoserine lactone (AHL)-dependent quorum sensing (QS). Plasma exposure of AHLs reduced the ability of such molecules to elicit a QS response in bacterial reporter strains in a dose-dependent manner. Short exposures (30-60 s) produce of a series of secondary compounds capable of eliciting a QS response, followed by the complete loss of AHL-dependent signalling following longer exposures. UPLC-MS analysis confirmed the time-dependent degradation of AHL molecules and their conversion into a series of by-products. FT-IR analysis of plasma-exposed AHLs highlighted the appearance of an OH group. In vivo assessment of the exposure of AHLs to plasma was examined using a standard in vivo model. Lettuce leaves injected with the rhlI/lasI mutant PAO-MW1 alongside plasma treated N-butyrylhomoserine lactone and n-(3-oxo-dodecanoyl)-homoserine lactone, exhibited marked attenuation of virulence. This study highlights the capacity of atmospheric pressure non-thermal plasma to modify and degrade AHL autoinducers thereby attenuating QS-dependent virulence in P. aeruginosa.The ability to generate chemically rich plasmas at or near ambient temperature and their demonstrated ability to influence biological processes has led to increasing interest in their use in a range of clinical interventions, and to the emergence of the nascent field of plasma medicine. The term 'plasma medicine' describes the emerging multidisciplinary field of study that examines the applicability and use of atmospheric pressure non-thermal plasmas in biomedical applications and more specifically in the treatment of viable tissue. The potential uses of atmospheric plasmas in biomedical applications include skin decontamination 1 , wound treatments 2,3 , surface disinfection 4,5 and invasive surgical treatments of tumours 6,7 . The physical and reactive chemistry of atmospheric pressure non-thermal plasma is derived from the production of an electric field capable of ionising air or a carrier gas such as helium/argon at atmospheric pressure. This ionisation process leads to the formation of photons, electrons, reactive species, electromagnetic energy and charged particles at a low temperature (sub 60 °C) 8 . Ambient temperatures are possible due to the inefficient transfer of energy between gas particles and electrons 9 . The efficacy of non-thermal plasma in proposed applications ranging from treatment of solid tumours, modification of cell proliferation and migration for wound healing, sterilisation and blood coagulation relies on the synergistic action of the localised generation of reactive oxygen and nitrogen species (RONS), electromagnetic energy, charged particles and UV li...

Clostridium difficile is a spore forming bacterium and the leading cause of colitis and antibiotic associated diarrhoea in the developed world. Spores produced by C. difficile are robust and can remain viable for months, leading to prolonged healthcare-associated outbreaks with high mortality. Exposure of C. difficile spores to a novel, non-thermal atmospheric pressure gas plasma was assessed. Factors affecting sporicidal efficacy, including percentage of oxygen in the helium carrier gas admixture, and the effect on spores from different strains representing the five evolutionary C. difficile clades was investigated. Strains from different clades displayed varying resistance to cold plasma. Strain R20291, representing the globally epidemic ribotype 027 type, was the most resistant. However all tested strains displayed a ~3 log reduction in viable spore counts after plasma treatment for 5 minutes. Inactivation of a ribotype 078 strain, the most prevalent clinical type seen in Northern Ireland, was further assessed with respect to surface decontamination, pH, and hydrogen peroxide concentration. Environmental factors affected plasma activity, with dry spores without the presence of organic matter being most susceptible. This study demonstrates that cold atmospheric plasma can effectively inactivate C. difficile spores, and highlights factors that can affect sporicidal activity.