Destruction of Bacterial Communities using Gas Discharge Plasma.

Summary form only given. Biofilms are microbial communities attached to an environmental surface and embedded in an extracellular glue-like matrix. Biofilms are involved in bacterial pathogenesis and attachment to surfaces such as pipes and medical devices. Microorganisms in biofilms show different properties compared to free-living cells; thus, conventional methods of killing bacteria are often ineffective with biofilms. Therefore, the ability to destroy these organisms is critical. The use of non-thermal plasmas potentially offers an effective alternative to conventional sterilization methods because plasmas contain a mixture of charged particles, chemically reactive species, and UV radiation and their decontamination potential relative to individual microorganisms is well established. However, to our knowledge, there is no information about the use of plasma to destroy bacterial biofilms. 4 and 7 day-old bacterial biofilms were produced using two bacterial species Rhizobium gallicum, Chromobaderium violaceum CV026 or a mixture of both bacteria. Gas discharge plasma was produced by using an AtomfloTM 250 reactor (Surfx Technologies, CA). An atmospheric pressure plasma was generated by using a He flow of 20.4 L/min and a secondary gas flow (N₂) of 0.305 L/min. Bacterial biofilms were exposed to plasma for different exposure times. Our results show that a 10-minute plasma treatment was able to kill 100% of the cells in most cases. Optical emission spectroscopy was used to study plasma composition and temperature which was then correlated with the effectiveness of killing. An emission spectrum from 200-450 nm will be presented. The characteristic features of the spectrum in the far ultraviolet are the NO gamma-bands near 250 nm and an OH band around 309 nm. The most prominent emission is due to the N₂ 2^nd positive band. Using the N₂ emissions, a plasma rotational temperature of 325 K was obtained with a margin of uncertai- ty of 20 K