Effect of plasma-activated water against E. coli and S. aureus: Influence of organic matter and impact on skin cell viability

Abstract: The study evaluated the antimicrobial efficacy of plasma-activated water (PAW), generated using a plasma bubble reactor, against Escherichia coli O157:H7 and Staphylococcus aureus in both planktonic and biofilm states. The physicochemical properties of PAW, including pH, electrical conductivity, and reactive oxygen and nitrogen species concentrations, were analysed immediately after production and after 24 and 48 h of storage at 4 °C. Additionally, the impact of organic load on PAW's antibacterial activity and its cytotoxic effects on human keratinocytes were investigated. To assess its stability, PAW’s antimicrobial activity after storage was also evaluated in the presence and absence of organic matter. PAW treatment resulted in a significant reduction in bacterial counts, achieving inactivation below the detection limit (1 log CFU/mL) within 20 min for both planktonic and biofilm states. However, the presence of organic matter significantly impaired PAW’s antibacterial efficacy, with higher organic loads leading to significantly diminished bacterial inactivation. PAW stored for 24 h maintained strong antimicrobial activity, which declined after 48 h; the presence of organic matter further reduced its efficacy across all time points. Importantly, PAW’s exposure did not induce cytotoxic effects on human keratinocytes at treatment durations of up to 30 min. These findings highlight the potential of PAW as a sustainable disinfection strategy, demonstrating robust antimicrobial activity against Gram-negative and Gram-positive foodborne pathogens while maintaining biocompatibility. Further research is required to enhance PAW’s efficacy in complex environments with organic contamination to enhance its practical applications in agri-food settings. Key points: • PAW effectively inactivated E. coli and S. aureus in planktonic and biofilm states. • PAW antimicrobial activity is reduced in the presence of organic matter. • PAW showed minimal cytotoxic effects on human keratinocytes.