Antimicrobial mechanism of in-situ plasma activated water treatment of pathogenic Escherichia coli and Staphylococcus aureus biofilms

Aims: This study investigated the efficacy and mechanisms of inactivation of against Escherichia coli UTI89 and Staphylococcus aureus NCTC8325 through an in-situ plasma-activated water (PAW) treatment. Methods and Results: PAW was prepared by discharging atmospheric pressure cold plasma beneath the surface of sterile distilled water. The study investigated the inactivation of biofilm cells and biofilm matrix. A complete killing of biofilm cells was achieved on both of E. coli (6.76 +/- 0.01 log CFU/mL) and S. aureus (6.82 +/- 0.02 log CFU/mL). This process happened earlier in S. aureus. Simultaneously, PAW treatment disrupted the biofilm structure, inducing a significant reduction in general biofilm biomass and extracellular polymer substances (EPS) matrix. With the disruption of EPS, PAW was enabled to further interact with the bacterial membrane, causing a significant increase in membrane permeability and disrupted membrane structure. Finally, PAW treatment led to a significant accumulation of intracellular reactive oxygen and nitrogen species within the biofilm cells. Conclusions: Collectively, these findings indicate that PAW effectively inactivates biofilms by mechanically targeting the biofilm EPS matrix and biofilm cells in both gram-negative and gram-positive bacteria.