The Role of Different Atmospheric Pressure Plasma Treatments for Inactivation of Bacteria Biofilmson Stainless Steel

Abstract

The objective of this study was to investigate the optimum conditions of inactivation efficiency of various atmospheric pressure plasma (APP) treatment methods to biofilms and furthermore, the inactivation mechanism of optimized APP treatment was investigated. Listeria monocytogenes (Gram-positive bacteria) and Escherichia coli O157:H7 (Gram-negative bacteria) biofilms were formed on stainless steel, widely used material for various utensils in food industry. Then, the biofilms were treated by four different methods of plasma treatment for 10 min: 1) direct plasma treatment (Direct-P)

2) plasma treatment dissolved in distilled water (DW-P), 3) 100 ppm of sodium chloride (NaCl-P), and 4) 100 ppm of sodium hypochlorite (NaOCl-P). No significant difference was shown in the reduction number (log CFU/cm2) of L. monocytogenes biofilms by different plasma treatment methods. However, the reduction number of E. coli O157:H7 was effective in order as NaOCl-P (3.45 log) > Direct-P (2.26 log) = NaCl-P (2.07 log) = DW-P (1.96 log). In NaOCl-P environment, the concentrations of hydroxyl radicals and peroxynitrite were the highest among the different methods of plasma treatment, indicating that these chemical species play a major role in inactivation of pathogenic bacteria in biofilms. Therefore, NaOCl-P is the optimum plasma treatment methods for inactivation of E. coli O157:H7 biofilms formed on stainless steel. In addition, the merit of using lower concentration of NaOCl than typical practice in industry can be achieved.