Antimicrobial mechanism and the effect of atmospheric pressure N<sub>2</sub> plasma jet on the regeneration capacity of <i>Staphylococcus aureus</i> biofilm

<p>This study systematically assessed the inactivation mechanism on <i>Staphylococcus aureus</i> biofilms by a N<sub>2</sub> atmospheric-pressure plasma jet and the effect on the biofilm regeneration capacity from the bacteria which survived, and their progenies. The total bacterial populations were 7.18 ± 0.34 log10 CFU ml<sup>−1</sup> in biofilms and these were effectively inactivated (>5.5-log10 CFU ml<sup>−1</sup>) within 30 min of exposure. Meanwhile, >80% of the <i>S. aureus</i> biofilm cells lost their metabolic capacity. In comparison, ∼20% of the plasma-treated bacteria entered a viable but non-culturable state. Moreover, the percentage of membrane-intact bacteria declined to ∼30%. Scanning electron microscope images demonstrated cell shrinkage and deformation post-treatment. The total amount of intracellular reactive oxygen species was observed to have significantly increased in membrane-intact bacterial cells with increasing plasma dose. Notably, the N<sub>2</sub> plasma treatment could effectively inhibit the biofilm regeneration ability of the bacteria which survived, leading to a long-term phenotypic response and dose-dependent inactivation effect on <i>S. aureus</i> biofilms, in addition to the direct rapid bactericidal effect.</p>