Disinfection is an operation that makes it possible to fight against the proliferation of bacteria and to temporarily eliminate some microorganisms. Traditionally, decontamination methods are based on the use of high temperature or chemical compounds (i.e.: chlorine and derivatives). But depending on the field of applications, theses traditional sanitation methods can be unsatisfactory because of effluents to be treated or heat sensitive surfaces. Moreover, many studies have demonstrated that traditional sanitation methods cannot completely eradicate microorganisms from food-processing surfaces [1] [2] . That is why the use of cold atmospheric pressure plasma is of great of interest. It offers rapid antimicrobial action against a broad spectrum of pathogens, while minimally affecting the exposed surface. Furthermore, it is environmentally friendly and requires no consumables except some gas (Ar, O₂ or air) [2] . These plasmas can be produced with different sources like corona discharges, Dielectric Barrier Discharges (DBD, planar or cylindrical configuration) or plasma jets working at different frequencies, radio-frequencies or microwaves [3] - [11] . Plasma torches work in open air or in controlled atmosphere. They are very versatile systems which find applications in a wide variety of fields such as the production of thin layers, surface modification but they are increasingly used for surface decontamination [3] .

Inactivation of micro-organisms is believed to be due to species produced in the plasma: mainly by radicals and reactive oxygen and nitrogen species, also called RONS [11] - [16] (OH, O, O₃, NO…) and charged ones ( O 2 − , NO 3 − …), affecting the cell membranes. UV can also create damages, especially UV C (220 - 280 nm) [12] [14] . The time of exposure influences the efficiency of the treatment [1] [16] [17] and the influence of the process parameters and the specific action of species and UV rays are still under discussion [16] [18] [19] [20] [21] .

Escherichia coli abbreviated E. coli is commonly used in biological experiments thanks to its ability to reproduce very quickly (every 20 minutes) and to the knowledge accumulated on its genome, its physiological properties and its metabolism. Whatever the means of treatment, bacteria die when cell membranes are broken or when DNA (deoxyribonucleic acid) is damaged [18] . The application of a treatment results in decontamination, disinfection or sterilization depending on the intensity (Table 1). A reduction log of at least 4 or 5 is generally sought, to have a suitable disinfection process.

The plasma source used in this study is TIA (Torche à Injection Axiale), it works with microwaves, in open air and the plasma forming gas is argon. It offers a wide range of working conditions, in terms of microwave power, gas flow rate, distance to the substrate and injection of additional gas or vapour. The TIA has already been used to deposit thin layers of crystallized TiO₂ [22] from TTIP precursor. For this, relatively high microwave power and low working distance allowing to transfer enough energy were selected to get in situ crystallization of TiO₂. The oxygen present in the TiO₂ comes from the ambient air. The power of plasma dissociates molecules (O₂, N₂) from the air to form reactive