Kinetics and microscopic studies of plasma-assisted biofilm destruction

Summary form only given. Biofilms are microbial communities attached to either an inert or living surface and encased in an exopolysaccharidic matrix also including a small amount of proteins and nucleic acids. Bacteria aggregated in a biofilm behave in a different way compared to free, planktonic cells. In the former, there are cooperative interactions among cells, thus; conventional disinfection methods are often ineffective with biofilms. The use of gas discharge plasmas is a potential solution to this problem since plasmas contain a mixture of charged particles, chemically reactive species, and UV radiation, individually known as effective killing agents. We have previously reported the use of plasma to destroy bacterial biofilms. Four day old biofilms were produced using Chromobacterium violaceum, a gram negative bacterium commonly present in soil and water. Gas discharge plasma was produced by using an AtomfloTM 250 reactor (Surfx Technologies, CA). An atmospheric pressure plasma jet was generated by using He and N₂ as a secondary gas. Biofilms were exposed to plasma for different periods of time, then disaggregated by sonication and processed to determine the kinetics of the killing process. For microscopy studies, biofilms underwent the same procedure and cells were examined using atomic force (AFM) and fluorescence microscopy. Optical emission spectroscopy was used to study plasma composition. Our results show that after a 10-minute plasma treatment, almost 100% of the viable cells are removed. The kinetics show a rapid initial decline in CFU/mL followed by a much slower subsequent decline with D-values that are longer than for the inactivation of planktonic organisms. Fluorescence microscopy and AFM confirmed these results and suggest that cells may undergo cell wall damage after plasma treatment. These results indicate the potential of plasma as an alternative way for biofilm removal