Sequential effect of phages and cold nitrogen plasma against Escherichia coli O157:H7 biofilms on different vegetables

Escherichia coli O157:H7 (E. coli O157:H7) is one of the most common pathogens in fresh vegetables and fruits, and most of the diseases produced by E. coli O157:H7 are associated with biofilms. Cold nitrogen plasma (CNP) is a cold sterilization technique which has no residue. However to completely eliminate the biofilm on the surface of vegetables the processing power and time of CNP have to be enhanced, which will impact on the quality of fruits and vegetables. Thus the sequential treatment of CNP and phage techniques was engineered in this study. Compared to treatment performed separately, sequential treatment not only had more mild treatment conditions as 400 W CNP treatment for 2 min and 5% phage treatment for 30 min, but also exhibited more remarkable effect on eradicating E. coli O157:H7 biofilms in vitro and on vegetables. The population of E. coli O157:H7 was approximately reduced by 2 log CFU/cm2 after individual treatment of 5% phages for 30 min or 500 W CNP for 3 min. While the sequential treatment of CNP (400 W, 2 min) and phages (5%, 30 min) reduced the E. coli O157:H7 viable count in biofilm by 5.71 log CFU/cm2. Therefore, the sequential treatment holds a great promise to improve the current treatment systems of bacterial contamination on different vegetable surfaces.