Gram positive and Gram negative bacteria differ in their sensitivity to cold plasma
Anne Mai-Prochnow1, Maryse Clauson1,2, Jungmi Hong1,3
1CSIRO Manufacturing, PO Box 218, Lindfield NSW 2070 Australia.
Scientific Reports
|December 10, 2016
Summary
Cold atmospheric-pressure plasma (CAP) effectively kills bacteria, with efficacy linked to cell wall thickness. Thicker walls in Gram-positive bacteria like Bacillus subtilis show more resistance to CAP treatment than thinner walls in Gram-negative species.
Area of Science:
- Microbiology
- Plasma Physics
- Biophysics
Background:
- Cold atmospheric-pressure plasma (CAP) is an emerging technology for antimicrobial applications.
- The precise mechanisms underlying CAP's antimicrobial activity are not fully understood.
- Bacterial cell wall characteristics are known to influence susceptibility to various antimicrobial agents.
Purpose of the Study:
- To investigate the correlation between bacterial cell wall thickness and the efficacy of cold atmospheric-pressure plasma (CAP).
- To explore how cell wall properties influence CAP's antimicrobial activity across different bacterial species and growth conditions.
Main Methods:
- Exposure of bacterial biofilms and planktonic cultures (Gram-positive and Gram-negative species) to CAP for 10 minutes.
- Measurement of bacterial reduction using log10 reduction.
- Analysis of bacterial cell wall thickness using nanometer measurements.
- Characterization of plasma emission spectra to identify reactive species (e.g., OH, O).
Main Results:
- Bacterial inactivation by CAP was directly correlated with cell wall thickness.
- Gram-positive Bacillus subtilis (55.4 nm cell wall) exhibited high resistance to CAP, with <1 log10 reduction.
- Gram-negative Pseudomonas aeruginosa (2.4 nm cell wall) biofilms were nearly eradicated under identical CAP treatment.
- Planktonic Gram-negative bacteria showed greater CAP susceptibility than Gram-positive bacteria.
- Mixed-species biofilms demonstrated higher resistance in Gram-positive species, though co-cultured P. aeruginosa showed increased overall resistance.
Conclusions:
- Bacterial cell wall thickness is a significant factor determining CAP efficacy.
- While cell wall thickness correlates with inactivation times, other factors like cell membranes and biofilm matrix likely contribute to CAP resistance.
- The presence of reactive oxygen and hydroxyl species in CAP suggests a mechanism involving structural cell wall damage.
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