Evaluating the Efficacy of Dielectric Barrier Discharge Plasma Against Planktonic and Biofilm Cultures of Staphylococcus aureus

Background.It is well-documented that numerous pathogenic microorganisms present in hospital settings exhibit diminished susceptibility to various biocidal agents, including but not limited to hydrogen peroxide, alcohols, chlorhexidine, iodophors, triclosan, and benzalkonium compounds. Previous reports have also highlighted the cross-resistance between biocide exposure and bacterial resistance to antibiotics. Therefore, it is necessary to search for effective methods of pathogen eradication. One of such effective methods is nonthermal plasma. It seems that due to the complex and diverse mechanisms of pathogen destruction, the development of bacterial resistance/tolerance to this eradication method is unlikely.

The aim of this study was to evaluate the effect of sublethal exposures of S. aureus to nonthermal plasma on some cell surface properties, biofilm formation efficiency, and the possibility of inducing tolerance of pathogenic bacteria to this biocidal technique.

Methods. Plasma inactivation of S. aureus inoculated on the surface of glass plates was performed using a DBD reactor operating at atmospheric pressure with air as working gas. The effects of multiple exposures to sublethal doses of plasma on the ability of cells to auto-aggregate, surface hydrophobicity, the ability to form biofilm on different surfaces, and changes in decimal reduction time (D) were assessed.

Results. Exposure of planktonic bacteria to nonthermal plasma for 2 min and 11 s results in 90% bacterial mortality (D). Destruction of the biofilm formed on the glass surface turned out to be more difficult. It was shown that the auto-aggregation properties and the hydrophobicity of cells significantly decreased after plasma treatments compared to control cells and the degree of these changes increased with the number of exposures to plasma. These changes in the surface structures of bacteria suggested that the ability of these pathogens to form biofilms may be limited. Our results showed that DBD plasma remained an effective biocidal method even after multiple exposures.