Bioelectrostatics Research Centre

Use of volatile additives to increase the antimicrobial efficacy of a

corona discharge

Dr Lindsey GauntBioelectrostatics Research Centre

School of Electronics and Computer Science

University of Southampton, UK

Bioelectrostatics Research Centre

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

• Aim; rationale

• Methods

• Results

• Discussion

• Applications and further work

Bioelectrostatics Research Centre

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 E. coli

• Enhance effects using volatile additives including essential oils

Bioelectrostatics Research Centre

Methods

• Test organisms were 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

Bioelectrostatics Research Centre

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

• 50l of either ethyl alcohol, cinnamon oil or tea tree oil

Direction of air flow

Ground electrode

Corona electrode

Mini crucible for volatiles

Bacterial plate

150mm

• Mean cfu counts compared • Standardised to 250• Mann-Whitney-U tests

Bioelectrostatics Research Centre

0

50

100

150

200

250

300

Alo

ne

Eth

ylA

lco

ho

l

Te

a tr

ee

oil

Cin

na

mo

no

il Alo

ne

Eth

ylA

lco

ho

l

Te

a tr

ee

oil

Cin

na

mo

no

ilcontrol non-ionised Ionised

Me

an

CF

U

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

Bioelectrostatics Research Centre

Survivorship of S. aureus following exposure to ionised and non-ionised regimes

0

50

100

150

200

250

300Al

one

Eth

ylAl

coho

l

Cin

nam

onoi

l Alon

e

Eth

ylAl

coho

l

Cin

nam

onoi

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control non-ionised Ionised

Mea

n C

FU

• 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

Bioelectrostatics Research Centre

SummaryNon-ionised

Air

Volatiles

Ionised

No effect

Vapour action

Cinnamon oil no effect vs. E.coli

Air

Volatiles

Ionic action

Ionised volatiles

E. coli least susceptible

Tea tree oil reduced ionic disinfection

Oils increased efficacy esp. E. coli

Bioelectrostatics Research Centre

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.

Bioelectrostatics Research Centre

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