Use of volatile additives to increase the antimicrobial efficacy of a corona discharge

1. Use of volatile additives to increase the antimicrobial efficacy of a corona discharge Dr Lindsey Gaunt Bioelectrostatics Research Centre School of Electronics and Computer Science University of Southampton, UK

2. Use of volatile additives to increase the antimicrobial efficacy of a corona discharge • Aim; rationale • Methods • Results • Discussion • Applications and further work

3. E. coli Introduction • Electrical discharges historically used in disinfection. • Intense plasma exposure for surface disinfection • Broad spectrum sterilisation of biological media and surfaces • Reactive oxygen species oxidise membrane macromolecules • Electrical corona in nitrogen • Effective concentration of ions and charged particles • Enhance effects using volatile additives including essential oils

4. Methods • Test organismswere Escherichia coli and Staphylococcus aureus • Enclosed booths of 0.5m3 • E. coli exposed for 30 minutes, S. aureus exposed for 10 minutes • Agar plates S. aureus

5. Corona electrode Ground electrode Mini crucible for volatiles 150mm Direction of air flow Bacterial plate Methods (cont.) Electrical corona driven ion wind Fan – non-ionised air flow Control – unexposed plates Current at plate of 10pA and ozone concentration of 0.2ppm 50l of either ethyl alcohol, cinnamon oil or tea tree oil Mean cfu counts compared Standardised to 250 Mann-Whitney-U tests

6. Survivorship of E. coli following exposure to ionised and non-ionised regimes Non-ionised air and cinnamon had no effects Viability was reduced by ethyl alcohol (19%) and tea tree oil (45%) Ionisation reduced viability by 65% Mortality was increased to 89% with addition of ethyl alcohol and 92% with cinnamon oil Tea tree oil reduced ionic efficacy

7. Survivorship of S. aureus following exposure to ionised and non-ionised regimes Non-ionised air reduced viability by 23% Ethyl alcohol and cinnamon oil reduced viability by 28% and 45% respectively Ionisation reduced viability by 74% Mortality was increased to 82% with addition of either ethyl alcohol or cinnamon oil

8. Summary Ionised Non-ionised No effect Air Air Ionic action E. coli least susceptible Volatiles Volatiles Vapour action Ionised volatiles Oils increased efficacy esp. E. coli Cinnamon oil no effect vs. E.coli Tea tree oil reduced ionic disinfection

9. Conclusion • Enhanced antibacterial activity through a reaction in the corona discharge with volatile molecules • Additive effect seen between ionic and volatile disinfection (ethyl alcohol and cinnamon oil (E. coli)) • Tea tree oil generates less effective species • Gram-negative bacteria (E. coli) are less susceptible to ionisation and volatiles than Gram-Positive (S. aureus) • Membrane damage invoked for ionic disinfection and essential oil effects; treatments compliment each other.

10. Applications and further work • Proof of concept • Aerial disinfection • Optimise, characterise and scale up • Pathogenic organisms • Understand issues • Heating, ventilation and air conditioning systems • Protection for public buildings, offices, medical environments and animal rearing facilities