Aims: The study aimed to investigate the inactivation efficacy and mechanisms of plasma activated water (PAW) on selected bacteria in planktonic state.
Methods and results: Plasma activated water was generated using an atmospheric cold plasma jet at 15, 22 and 30 kV for 5 min. Escherichia coli, Listeria innocua, Staphylococcus aureus, Aeromonas hydrophila, Pseudomonas fluorescens and Shewanella putrefaciens were selected as the representative bacterial species. Each bacterial suspension was inoculated into PAW immediately after generation, and the viable counts at different exposure times of 0·5, 1, 3, 5 and 24 h during 4°C storage were measured to determine the inactivation efficacy. Scanning electron microscopy images of the bacteria were conducted to examine the structural changes. Physicochemical properties of PAW, including pH, conductivity, oxidation reduction potential (ORP), and reactive species of H2 O2 , NO2 - and NO3 - were measured. The results demonstrated that inactivation efficacy was in positive correlation with voltage and exposure time. Gram-negative bacteria were more susceptible to PAW than Gram-positive bacteria. Morphology damage was observed for all the bacterial species. PAW was significantly acidified, conductivity and ORP were significantly increased, and reactive species were detectable after 48 h.
Conclusions: This study offered a better understanding of the inactivation mechanisms of PAW, and the inactivation efficacy can be affected by voltage, exposure time and bacterial species.
Significance and impact of the study: This study demonstrated the potential usage of PAW as an alternative disinfectant.
Keywords: inactivation efficacy; inactivation mechanisms; pH; physicochemical properties; plasma activated water; reactive species.
© 2020 The Society for Applied Microbiology.