Potential cellular targets and antibacterial efficacy of atmospheric pressure non-thermal plasma

Atmospheric pressure non-thermal plasma (APNTP) has been gaining increasing interest as a new alternative antibacterial approach. Although this approach has demonstrated promising antibacterial activity, its exact mechanism of action remains unclear. Mechanistic elucidation of the antimicrobial activity will facilitate development and rational optimisation of this approach for potential medical applications. In this study, the antibacterial efficacy of an in-house-built APNTP jet was evaluated alongside an investigation of the interactions between APNTP and major cellular components in order to identify the potential cellular targets involved in plasma-mediated bacterial destruction mechanisms. The investigated plasma jet exhibited excellent, rapid antibacterial activity against a selected panel of clinically significant bacterial species including Bacillus cereus, meticillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Pseudomonas aeruginosa, all of which were completely inactivated within 2 min of plasma exposure. Plasma-mediated damaging effects were observed, to varying degrees, on all of the investigated cellular components including DNA, a model protein enzyme, and lipid membrane integrity and permeability. The antibacterial efficacy of APNTP appears to involve a multiple-target mechanism, which potentially reduces the likelihood of emergence of microbial resistance towards this promising antimicrobial approach. However, cellular membrane damage and resulting permeability perturbation was found to be the most likely rate-determining step in this mechanism.