Non-thermal plasma mills bacteria: Scanning electron microscopy observations

Abstract

Non-thermal plasmas hold great promise for a variety of biomedical applications. To ensure safe clinical application of plasma, a rigorous analysis of plasma-induced effects on cell functions is required. Yet mechanisms of bacteria deactivation by non-thermal plasma remain largely unknown. We therefore analyzed the influence of low-temperature atmospheric plasma on Gram-positive and Gram-negative bacteria. Using scanning electron microscopy, we demonstrate that both Grampositive and Gram-negative bacteria strains in a minute were completely destroyed by helium plasma. In contrast, mesenchymal stem cells (MSCs) were not affected by the same treatment. Furthermore, histopathological analysis of hematoxylin and eosin-stained rat skin sections from plasma-treated animals did not reveal any abnormalities in comparison to control ones. We discuss possible physical mechanisms leading to the shred of bacteria under non-thermal plasma irradiation. Our findings disclose how helium plasma destroys bacteria and demonstrates the safe use of plasma treatment for MSCs and skin cells, highlighting the favorability of plasma applications for chronic wound therapy. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4907624]Deactivation of bacteria and control of cellular nanomechanics can be done by different physical factors, including: mechanical forces, 1 laser irradiation, 2 high-gradient magnetic field, 3-5 pulses of electric field, 6 ultrasound, 7 and atmospheric non-thermal plasma. 8,9 However, the mechanisms of these effects and factors related to regulation of bacteria proliferation and death have been poorly investigated and not fully understood. Interactions between bacteria (cells) and plasmas can be carried out by means of any of plasma's agents: neutral gas, charged particles, excited atoms/molecules, reactive species (such as NO, O 3 , OH, and O 2 À ), UV light, electrical field, and ion bombarding. Thus, various constituents of plasma can affect biological, physical, and chemical processes in mammalian cell cultures, tissue, and microorganisms.In the last several decades, the problem of antibiotic resistance emerged as a rapidly growing public health issue. 10 Therefore, there is an indispensable need for the design and development of novel alternatives to antibiotics. In this regard, non-thermal plasma represents an important and effective alternative approach in overcoming resistant microorganisms. 11,12 The use of non-thermal atmospheric pressure plasma devices in clinical practice requires operating regimes that can be easily controlled and adjusted during treatments. Moreover, some side effects of the developed plasma devices, in particular, on the respiratory organs or the overheating of healthy tissues, can be expected. These unfavorable effects can be reduced by tuning of the physical properties of plasma generators. A burst of studies indicate a great potential of low temperature plasmas use in a wide variety of biological and medical applications, 12 specifically in wound healing. 9,13 Concomitantl...

Non-thermal air plasma promotes the healing of acute skin wounds in rats

“…The wound area was significantly more reduced in the rats treated with NTP than in that of the untreated rats on day 7, and also histological analysis confirmed an enhanced epithelisation and a reduced granulation tissue area after plasma treatment. Respectively, improved wound contraction after the plasma treatment has also been confirmed in other studies using NTP generated from argon, helium or nitrogen1678910111213141516171830.…”

“…. We have previously demonstrated, that under plasma treatment, mechanically rigid bacterial wall structures can be destroyed due to internal electrostatic pressure raised, as a result of ion accumulation9. Depending on the plasma dose and voltage value producing the plasma discharges, NTP may trigger either programmed cell death or physical destruction of the bacteria10.…”

Chemically different non-thermal plasmas target distinct cell death pathways

“…Additionally, according to the SCCP European Commission Report 0949/05, the maximum allowed UV dose rate is 50 μW/cm 2 , which is one order of magnitude higher than in our case 27 . Moreover, we 28 and others 29, 30 have previously shown that the UV radiation is not the dominant biological agent of non-thermal plasmas of such ion density and energy. Detailed NTP treatment procedure and plasma system characterization is given in the Materials and Methods section.…”

Nonthermal Atmospheric Plasmas in Dental Restoration

“…Plasma treatment of tooth cavities or dental surfaces allows us to avoid contamination, actively fight bacterial infections, offer additional cleaning to the decayed matters in the tooth cavities, and prepare/ engineer the dentin and adhesive surface/interface for strong and durable bonding to composite restorative materials with a cohesive treatment process. A broad spectrum of bacteria can be deactivated/destructed by NTAP, including Gram-negative Pseudomonas aeruginosa and Escherichia coli and Gram-positive Staphylococcus aureus, Bacillus subtilis, and Micrococcus luteus Yu et al 2007;Zhou et al 2010;Alkawareek et al 2014;Lunov et al 2015). It was found that NTAP's antibacterial activity was not due to UV emission (Lunov et al 2015) but rather to reactive oxygen species, which led to oxidative damages to cell membrane, DNA, and proteinaceous enzymes (Alkawareek et al 2014).…”

“…A broad spectrum of bacteria can be deactivated/destructed by NTAP, including Gram-negative Pseudomonas aeruginosa and Escherichia coli and Gram-positive Staphylococcus aureus, Bacillus subtilis, and Micrococcus luteus Yu et al 2007;Zhou et al 2010;Alkawareek et al 2014;Lunov et al 2015). It was found that NTAP's antibacterial activity was not due to UV emission (Lunov et al 2015) but rather to reactive oxygen species, which led to oxidative damages to cell membrane, DNA, and proteinaceous enzymes (Alkawareek et al 2014). Thus, the antibacterial efficacy of NTAP was tunable by adjusting oxygen feeding to the plasma-generating devices Yu et al 2007;Zhou et al 2010).…”