Synergistic antibacterial effects of treatments with low temperature plasma jet and pulsed electric fields

Inactivation of Staphylococcus aureus by a non-thermal argon operated plasma jet and by microsecond pulsed electric fields (PEF) was investigated. The different methods were either applied by themselves or in combination with each other. Treatments with plasma alone or pulsed electric fields alone were found to result in significant but not complete inactivation. A 2-log reduction was observed for the longest plasma exposure time of 3 min or for the application of 300 consecutive electric field pulses with 100-μs duration and 15-kV/cm amplitude. For the combined treatment with non-thermal plasma and pulsed electric fields, significant synergistic antibacterial effects were observed when samples were treated with plasma first. However, only an additive or at most a slight synergistic effect was observed when samples were first treated with pulsed electric fields instead. The acidification of the bacteria suspension after plasma treatment is likely responsible for the support of subsequent reaction mechanisms that are induced by exposures to pulsed electric fields and is hence the reason for the observed synergy.