The antimicrobial efficacy of plasma-activated water against Listeria and E. coli is modulated by reactor design and water composition

Abstract

Aims: This study aimed to compare the efficacy of plasma-activated water (PAW) generated by two novel plasma reactors against pathogenic foodborne illness organisms. Methods and results:The antimicrobial efficacy of PAW produced by a bubble spark discharge (BSD) reactor and a dielectric barrier discharge-diffuser (DBDD) reactor operating at atmospheric conditions with air, multiple discharge frequencies and Milli-Q and tap water, was investigated with model organisms Listeria innocua and Escherichia coli in situ. Optimal conditions were subsequently employed for pathogenic bacteria Listeria monocytogenes, E. coli and Salmonella enterica. DBDD-PAW reduced more than 6-log of bacteria within 1 min. The BSD-PAW, while attaining high log reduction, was less effective. Analysis of physicochemical properties revealed that BSD-PAW had a greater variety of reactive species than DBDD-PAW.Scavenger assays designed to specifically sequester reactive species demonstrated a critical role of superoxide, particularly in DBDD-PAW.Conclusions: DBDD-PAW demonstrated rapid antimicrobial activity against pathogenic bacteria, with superoxide the critical reactive species. Significance and impact of study: This study demonstrates the potential of DBDD-PAW produced using tap water and air as a feasible and cost-effective option for antimicrobial applications, including food safety.

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“…The superoxide anion (•O2 -) has previously been demonstrated to be critical for the antimicrobial activity of the DBDD-PAW (29), and this was confirmed in the current study where the addition of tiron, a •O2scavenger, significantly reduced the antimicrobial activity of the DBDD-PAW. •O2has a short half-life and a negative charge when in a solution with a neutral pH (57) which would typically prevent it from passing through the membrane of bacterial cells (58).…”

“…Our previous work had identified . O2as a critical reactive species for the antimicrobial power of the DBDD-PAW (29). We investigated the antimicrobial role of .…”

“…For example, current research frequently uses purified or distilled water as the PAW substrate (27, 28). However, tap water is more reflective of current (and potential future) industry practice, even though it may produce lower antimicrobial power and less reproducible results than purified or distilled water (29). Similarly, current PAW research frequently uses discharge gases such as argon or oxygen in plasma generation.…”

“…In our previous work, we demonstrated rapid antimicrobial power against bacterial foodborne pathogens using a dielectric barrier discharge diffusor (DBDD) PAW system with tap water as the PAW substrate and air as the discharge gas (29). Physicochemical analysis of the PAW revealed that a DBDD reactor using tap water produced extremely low concentrations of reactive nitrogen species (NOx) and H 2 O 2 , and scavenger assays demonstrated that ·O 2 − was essential for the antimicrobial activity of this system.…”

The optimization of plasma activated water ( PAW ) generation and the inactivation mechanism of PAW on Escherichia coli

“…Previous study also reported that and 1 O 2 were two key reactive species which enhanced the E. coli inactivation effects of PAW substantially (Ma et al, 2020). Rothwell et al (2022) indicated that and/or downstream reactive species to be critical role for bactericidal effects of PAW, particularly in DBD plasma. Therefore, were likely to be one of the key factors for microorganism inactivation in PAW.…”