Assessment of plasma activated water antimicrobial activity on planktonic cells and wet biofilms of an Escherichia coli strain

Abstract

Background Plasma activated water (PAW) is a novel non-thermal disinfection technology in which an acidic environment is created due to the formation of reactive oxygen and nitrogen species coupled with changes in redox potential. For such reasons, PAW has such a composition that can possibly serve as a means for microbial disinfection in the food industry. Method PAW was generated at atmospheric pressure in an electrochemical cell equipped with a copper electrode. Each PAW sample was prepared following a 3 h of plasma discharge with water circulating, while air was used as a gas with a flow rate of 150 L/ h. Before each use, the pH and conductivity of the generated PAW were measured. Escherichia coli NCTC12900 was used in this study. Throughout the analysis, sterile distilled water was used as a control E.coli planktonic cells were exposed to PAW, and enumeration was performed at time intervals for 25 minutes. Additionally, biofilm assessments were also performed in which its formation was carried out on coupons made from stainless steel. A pre-attachment stage of 3 h was performed and subsequently coupons were immersed in the Tryptic Soy Broth for 48 hours at 37°C. Following the biofilm development, the coupons were exposed to PAW with contact periods of 0, 5, 10, 15 and 20 minutes. The detachment of biofilms was accomplished using sonication. Results After 25 minutes exposure to PAW, a reduction of 2.5 log CFU/mL was observed for the planktonic cells whilst, exposure to sterile distilled water caused a reduction of 0.10 log CFU/mL. Furthermore, a reduction of 2.5 log CFU/cm2 was observed after biofilm exposure to PAW for 20 minutes (maximum time studied), where a reduction of 0.96 log CFU/cm2 was obtained for the control case. Conclusion The research study suggests that PAW has a potential to be utilised as a means of disinfection on food contact surfaces, however, further research is needed to determine the contact time required to achieve higher disinfection rates.