Background: Salmonella species are the second most common bacterial cause of foodborne gastrointestinal disease. Humans can acquire Salmonella from contaminated food sources, like raw eggs, raw egg products and chicken meat, which are associated with >60% of outbreaks, representing a significant public health issue. Salmonellosis is generally a self-limiting disease, and antibiotics are reserved for only the most severe cases. The emergence and spread of multidrug-resistant strains calls for the development and implementation of alternative strategies to prevent foodborne disease.
We validated an innovative antimicrobial strategy using cold plasma technology to ensure food safety. Plasma is an ionised gas consisting of ions, free electrons and radicals. Plasma discharged in water (plasma-activated water; PAW) enriches water with reactive oxygen and nitrogen species, creating an antimicrobial environment.
Aim: To validate the efficacy of 5 PAW types against 4 different Salmonella typhimurium isolates.
Methods and results: The bactericidal effect of PAW was evaluated using time-kill curves. PAW types with the highest redox potential and lowest pH had the highest efficacy, eliminating culturable bacteria within 2.5 min of exposure. The antibiofilm effect of PAW was assessed by the Crystal Violet assay, AlamarBlue viability assay and in a 3D-biofilm model with real-time imaging (Bioflux flow system). Two types of PAW resulted in significant reduction of both biofilm biomass (up to 50% reduction, p<0.01) and biofilm viability (≥98% reduction, p<0.01) compared to the growth control. Results were confirmed by real-time imaging, showing substantial killing and partial removal of 3D-Salmonella biofilms after PAW exposure under flow conditions.
Conclusion: The bactericidal and antibiofilm capacity of specific PAW types against Salmonella isolates highlights their potential use as an alternative control strategy to reduce pathogen levels in the human food supply chain, reduce food spoilage, food loss and food poisoning.