Understanding of the interaction mechanisms between plasma produced atomic nitrogen and living matter – PLASMAVIV

The sterile state is a state defined as free from any living micro-organism, not spontaneously found in nature. It is needed in medicine to ensure a minimum risk of contamination for patients.
In France, a report from the Senate indicates that 6 to 7% of the hospitalizations are complicated by nosocomial infections. These infections are the cause of 9,000 deaths per year, 50% of them concerning patients not in danger when they enter the hospital. In all cases, they induce a longer hospital stay and an increased cost estimated nationally to several billions of Euros.
Moreover, following recent epidemiological works, it appeared that significant quantities of organic matter remain on the surface of instruments after conventional sterilization by autoclaving. These residues may contain highly toxic biomolecules such as bacterial endotoxins or even prion proteins, which must be eliminated as the pathogenic micro-organisms.
It is therefore clear that there is currently no means to respond effectively to the demands of quality and safety required for the decontamination of the reusable medical instrumentation.
Plasmas being able to simultaneously generate heat, emission of radiation and many chemical species active on organic matter from non-toxic gases, they are an ideal medium for decontamination. Two ways of treatment are possible, either by immersing the instruments in the discharge itself, or by subjecting them to its effluents, into the afterglow. If one wants to minimize the aggressiveness of the plasma treatment for the substrates (the same instrument can be decontaminated hundreds of times during its lifetime), the afterglow, although less rich in active species as the discharge, seems more appropriate.
By coupling mechanisms of UV irradiation and chemical etching, the processing time required for a reduction of 6 log (assimilated to a sterilization) of the initial population of the micro-organisms in the afterglow is around several tens of minutes while it is only a few seconds into the discharge. These results are generally obtained with oxygenated or fluorinated plasma gases, allowing to generate atomic species known for their high etching power, that will also interact and degrade the substrates on which the micro-organisms are present.
To avoid such problems, the “Plasmas Réactifs Hors Equilibre” team of the LAPLACE has worked for several years to develop a sterilization process using a microwave afterglow at reduced pressure without oxygen. It uses pure nitrogen for which the antibacterial activity of nitrogen atoms has already been established and did not induce damages to the exposed substrates. This work also showed that the mode of action of the nitrogen afterglow on the micro-organisms was a priori different from the one involved in decontamination by oxygen afterglows.
Preliminary studies initiated during a PEPS ST2I (PLASMAVIV 2008) have also highlighted the potential of nitrogen afterglows for the treatment of biomolecules. Removal rates of about 25 to 30% have been obtained with a standard protein (albumin) without any optimization of the afterglow and of the used biological protocol.
The objectives of the present project are therefore twofold :
1- improve the understanding of the interaction mechanisms between the nitrogen atoms and the micro-organisms through the study of interactions with various bacterial components: lipids, proteins, DNA, ...
2- demonstrate the applicability of nitrogen afterglows at reduced and atmospheric pressure for the elimination of micro-organisms and biomolecules.