Biofilm Destruction by RF High-Pressure Cold Plasma Jet

Abstract

Biofilms are bacterial communities embedded in a glue-like matrix mostly composed of exopolysaccharides and a small amount of proteins and nucleic acids. Conventional disinfection and sterilization methods are often ineffective with the biofilms since microorganisms within the biofilm show different properties from those in free planktonic life. The use of the gas discharge plasmas is a novel alternative since the plasmas contain a mixture of charged particles, chemically reactive species, and UV radiation. The four-day-old single-species biofilms were produced using Chromobacterium violaceum, a gram-negative bacterium commonly present in soil and water. The gas discharge plasma was produced by using an Atomflo 250 reactor (Surfx Technologies), and the bacterial biofilms were exposed to it for different periods of time. Our results show that a 10-min plasma treatment is able to kill almost 100% of the cells. The results show a rapid initial decline in the colony forming units per milliliter (phase one) that is followed by a much slower subsequent decline (phase two) of the D-values that are longer than the inactivation of the planktonic organisms, suggesting a more complex inactivation mechanism for the biofilms. Two hypotheses are offered to explain this biphasic behavior. Optical emission spectroscopy was used to study the plasma composition, and the role of the active species is discussed. These results indicate the potential of plasma as an alternative way for biofilm removal