title: Gram positive and Gram negative bacteria differ in their sensitivity to cold plasma.
abstract: Cold atmospheric-pressure plasma (CAP) is a relatively new method being investigated for antimicrobial activity. However, the exact mode of action is still being explored. Here we report that CAP efficacy is directly correlated to bacterial cell wall thickness in several species. Biofilms of Gram positive Bacillus subtilis, possessing a 55.4 nm cell wall, showed the highest resistance to CAP, with less than one log10reduction after 10 min treatment. In contrast, biofilms of Gram negative Pseudomonas aeruginosa, possessing only a 2.4 nm cell wall, were almost completely eradicated using the same treatment conditions. Planktonic cultures of Gram negative Pseudomonas libanensis also had a higher log10reduction than Gram positive Staphylococcus epidermidis. Mixed species biofilms of P. aeruginosa and S. epidermidis showed a similar trend of Gram positive bacteria being more resistant to CAP treatment. However, when grown in co-culture, Gram negative P. aeruginosa was more resistant to CAP overall than as a mono-species biofilm. Emission spectra indicated OH and O, capable of structural cell wall bond breakage, were present in the plasma. This study indicates that cell wall thickness correlates with CAP inactivation times of bacteria, but cell membranes and biofilm matrix are also likely to play a role.
authors.affiliation: CSIRO Manufacturing, PO Box 218, Lindfield NSW 2070 Australia.
authors.forename: Anne
authors.initials: A
authors.lastname: Mai-Prochnow
authors.affiliation: CSIRO Manufacturing, PO Box 218, Lindfield NSW 2070 Australia.|National Engineering School of Agronomy and Food Science, Nancy, France.
authors.forename: Maryse
authors.initials: M
authors.lastname: Clauson
authors.affiliation: CSIRO Manufacturing, PO Box 218, Lindfield NSW 2070 Australia.|School of Physics, University of Melbourne VIC 3010, Australia.
authors.forename: Jungmi
authors.initials: J
authors.lastname: Hong
authors.affiliation: CSIRO Manufacturing, PO Box 218, Lindfield NSW 2070 Australia.
authors.forename: Anthony B
authors.initials: AB
authors.lastname: Murphy
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D001128:Argon / Q000737:chemistry; D018441:Biofilms / Q000187:drug effects; D002473:Cell Wall; D006090:Gram-Negative Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D058626:Plasma Gases / Q000737:chemistry / Q000494:pharmacology*; D013057:Spectrum Analysis
chemical_list: D000900:Anti-Bacterial Agents; D058626:Plasma Gases; D001128:Argon