Antimicrobial activity of plasma activated water against E. coli NCTC 12900 planktonic cells and biofilms formed on polystyrene surfaces

Abstract

Background: Biofilm formation is the main cause contributing to an increase in foodborne illnesses. However, this may be prevented by using novel disinfection methods such as Plasma Activated Water (PAW), known for having strong antimicrobial properties. This study aims to develop bacterial biofilms under conditions similar to those encountered in the food industry, namely in polystyrene surfaces, and to evaluate the disinfection ability of PAW. Methodology: PAW was produced at atmospheric pressure using a copper electrochemical cell, and the pH of each PAW sample generated was measured. Escherichia coli NCTC 12900 was used throughout the study, whilst sterile distilled water was used as a control. Bacterial enumeration was performed on planktonic E. coli cells exposed to freshly prepared PAW for 0, 10, 20, 30, 40, 50, and 60 minutes. Biofilm evaluation was then carried out, with biofilm formation taking place on polystyrene surfaces. After the formation of wet and dry biofilms, these were exposed to PAW for 0, 5, 10, 15 and 20 minutes. Biofilm detachment was achieved by cell scraping. Results: The results obtained showed approximately a 5 log CFU/mL reduction of planktonic cells after being exposed to PAW for a total of 60 minutes. With regards to dry biofilm formation, the counts for both the PAW exposure and the control were consistently below the detection limit. On the contrary, for the wet biofilms, following 20 minutes of exposure to PAW, there was a 2.5 log CFU/cm2 reduction. Conclusion: This study indicates that PAW can be an effective disinfectant, however, its efficacy is compromised when studying biofilm forms. Furthermore, additional research is needed to establish whether PAW can be utilised by the food industries as a disinfectant, given that some of its components might exert toxic effects.