Benjamin Denis

Identification of the most efficient VUV/UV radiation for plasma based inactivation of Bacillus atrophaeus spores

The identification of sterilization agents is mandatory to achieve sterilization mechanisms in low-pressure discharges. A detailed account of each agent is required for improvements, development and establishment of plasma sterilization as an alternative to traditional sterilization processes. Sterilization agents are VUV and UV radiation, photodesorption producing volatile species and etching of spore coat and membrane. This work focuses on VUV and UV radiation as a sterilization agent of Bacillus atrophaeus spores. Four wavelength ranges are distinguished: the emission spectra above 300 nm, above 235 nm, above 112 nm and a full emission spectrum including active species. The range from 235 up to 300 nm without active species is identified to be the most capable for sterilizing Bacillus atrophaeus spores.

On the application of inductively coupled plasma discharges sustained in Ar/O2/N2 ternary mixture for sterilization and decontamination of medical instruments

Non-equilibrium low pressure-plasma discharges are extensively studied for their high potential in the field of sterilization and decontamination of medical devices. This increased interest in plasma discharges arises from, among other reasons, their capability not only to inactivate bacterial spores but also to eliminate, destroy or remove pathogenic biomolecules and thus to provide a one-step process assuring safety of treated instruments. However, recent studies have shown that optimal conditions leading to inactivation of spores and physical removal of pathogens differ significantly—the efficiency of spores sterilization is above all dependent on the UV radiation intensity, whereas high etching rates are connected with the presence of the etching agent, typically atomic oxygen. The aim of this contribution is to discuss and demonstrate the feasibility of Ar/N2/O2 low-pressure inductively coupled plasma discharges as an option to provide intense UV radiation while maintaining the high etching rates of biomolecules.

Separation of VUV/UV photons and reactive particles in the effluent of a He/O2 atmospheric pressure plasma jet

Cold atmospheric pressure plasmas can be used for treatment of living tissues or for inactivation of bacteria or biological macromolecules. The treatment is usually characterized by a combined effect of UV and VUV radiation, reactive species and ions. This combination is usually beneficial for the effectiveness of the treatment but it makes the study of fundamental interaction mechanisms very difficult. Here we report on an effective separation of VUV/UV photons and heavy reactive species in the effluent of a microscale atmospheric pressure plasma jet (μ-APPJ). The separation is realized by an additional flow of helium gas under well-defined flow conditions, which deflects heavy particles in the effluent without affecting the VUV and UV photons. Both components of the effluent, the photons and the reactive species, can be used separately or in combination for sample treatment. The results of treatment of a model plasma polymer film and vegetative Bacillus subtilis and Escherichia coli cells are shown and discussed. A simple model of the He gas flow and reaction kinetics of oxygen atoms in the gas phase and at the surface is used to provide a better understanding of the processes in the plasma effluent. The new jet modification, called X-Jet for its appearance, will simplify the investigation of interaction mechanisms of atmospheric pressure plasmas with biological samples.

Understanding of the importance of the spore coat structure and pigmentation in the Bacillus subtilis spore resistance to low-pressure plasma sterilization

Low-pressure plasmas have been evaluated for their potential in biomedical and defense purposes. The sterilizing effect of plasma can be attributed to several active agents, including (V)UV radiation, charged particles, radical species, neutral and excited atoms and molecules, and the electric field. Spores of Bacillus subtilis were used as a bioindicator and a genetic model system to study the sporicidal effects of low-pressure plasma decontamination. Wild-type spores, spores lacking the major protective coat layers (inner, outer, and crust), pigmentation-deficient spores or spore impaired in encasement (a late step in coat assembly) were systematically tested for their resistance to low-pressure argon, hydrogen, and oxygen plasmas with and without admixtures. We demonstrate that low-pressure plasma discharges of argon and oxygen discharges cause significant physical damage to spore surface structures as visualized by atomic force microscopy. Spore resistance to low-pressure plasma was primarily dependent on the presence of the inner, and outer spore coat layers as well as spore encasement, with minor or less importance of the crust and spore pigmentation, whereas spore inactivation itself was strongly influenced by the gas composition and operational settings.

Sterilization of beehive material with a double inductively coupled low pressure plasma

American Foulbrood is a severe, notifiable disease of the honey bee. It is caused by infection of bee larvae with spores of the gram-positive bacterium Paenibacillus larvae. Spores of this organism are found in high numbers in an infected hive and are highly resistant to physical and chemical inactivation methods. The procedures to rehabilitate affected apiaries often result in the destruction of beehive material. In this study we assess the suitability of a double inductively coupled low pressure plasma as a non-destructive, yet effective alternative inactivation method for bacterial spores of the model organism Bacillus subtilis on beehive material. Plasma treatment was able to effectively remove spores from wax, which, under protocols currently established in veterinary practice, normally is destroyed by ignition or autoclaved for sterilization. Spores were removed from wooden surfaces with efficacies significantly higher than methods currently used in veterinary practice, such as scorching by flame treatment. In addition, we were able to non-destructively remove spores from the highly delicate honeycomb wax structures, potentially making treatment of beehive material with double inductively coupled low pressure plasma part of a fast and reliable method to rehabilitate infected bee colonies with the potential to re-use honeycombs.

Etching of bacterial endospores of Bacillus subtilis in an inductively coupled low-pressure plasma

Low-pressure plasmas offer a rapid and efficient option for sterilization of pharmaceutical and medical objects. First commercial plasma sterilization reactors are approved by European Medicines Agency (EMA).1 On short time scales UV/VUV radiation was shown to be the main sterilization mechanism. In order to inactive heterogeneous contamination of microorganisms (i.e., multilayer arrangements of vegetative cells and bacterial endospores) sufficient etching is needed for plasma sterilization.

Investigation on the sterilization mechanisms of a double inductively coupled plasma

Gentile plastic materials used for medical implants are a challenge for common sterilization processes which are either too hot or toxic. Plasma sterilization promises a way to achieve cold, gentile and fast sterilization of medical objects. Different sterilization mechanisms inside a plasma are known: radicals, ion bombardment and radiation. Radicals etch the spore coat, ions with enough energy break bonds, UV and VUV photodesorption can produce volatile species in the spore coat. This can lead to cell death during proliferation. Additionally, radiation below 275 nm can cause strand breaks in the DNA. This contribution focuses on sterilization caused by radiation in the range of 110 - 450 nm. Sterilization results are presented to show the efficiency of optical emission as an important sterilization mechanism in plasmas.