Eradication of methicillin-resistant Staphylococcus aureus biofilms by surface discharge plasmas with various working gases

Surface discharge plasmas have advantages in various applications, such as the treatment of wound infections. However, the effects of surface discharge plasmas on biofilms have not been studied. In this study, the inactivation of methicillin-resistant Staphylococcus aureus biofilms by surface discharge plasmas with four working gases, namely, He + 1% air, Ar + 1% air, synthetic air, and natural air, was investigated to elucidate the correlation between the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) and the biofilm eradication performance. The experimental results demonstrated that the surface plasma with Ar + 1% air produced the highest concentrations of excited reactive species in gas phase and of and /.NO₂/ONOO^- in the liquid phase, while the surface plasma with synthetic air produced largest amount of and ¹O₂ in the liquid phase. For methicillin-resistant S. aureus biofilms, the inactivation effects of the surface plasmas with Ar + 1% air and natural air were similar and more pronounced compared with the other gases, while the inactivation effect of surface plasma with He + 1% air was the least pronounced. The biofilm inactivation and ROS penetration by He + 1% air plasma could be enhanced by a low concentration of nitrite and nitrate. Based on the results, it was proposed that plasma-generated long-lived species promoted the penetration of reactive species in biofilms, and the penetrated ROS and RNS jointly contributed to the inactivation of methicillin-resistant S. aureus biofilms.