Bactericidal effects of non-thermal argon plasma in vitro, in biofilms and in the animal model of infected wounds

Abstract

Non-thermal (low-temperature) physical plasma is under intensive study as an alternative approach to control superficial wound and skin infections when the effectiveness of chemical agents is weak due to natural pathogen or biofilm resistance. The purpose of this study was to test the individual susceptibility of pathogenic bacteria to non-thermal argon plasma and to measure the effectiveness of plasma treatments against bacteria in biofilms and on wound surfaces. Overall, Gram-negative bacteria were more susceptible to plasma treatment than Gram-positive bacteria. For the Gramnegative bacteria Pseudomonas aeruginosa, Burkholderia cenocepacia and Escherichia coli, there were no survivors among the initial 10 5 c.f.u. after a 5 min plasma treatment. The susceptibility of Gram-positive bacteria was species-and strain-specific. Streptococcus pyogenes was the most resistant with 17 % survival of the initial 10 5 c.f.u. after a 5 min plasma treatment. Staphylococcus aureus had a strain-dependent resistance with 0 and 10 % survival from 10 5 c.f.u. of the Sa 78 and ATCC 6538 strains, respectively. Staphylococcus epidermidis and Enterococcus faecium had medium resistance. Non-ionized argon gas was not bactericidal. Biofilms partly protected bacteria, with the efficiency of protection dependent on biofilm thickness. Bacteria in deeper biofilm layers survived better after the plasma treatment. A rat model of a superficial slash wound infected with P. aeruginosa and the plasma-sensitive Staphylococcus aureus strain Sa 78 was used to assess the efficiency of argon plasma treatment. A 10 min treatment significantly reduced bacterial loads on the wound surface. A 5-day course of daily plasma treatments eliminated P. aeruginosa from the plasma-treated animals 2 days earlier than from the control ones. A statistically significant increase in the rate of wound closure was observed in plasma-treated animals after the third day of the course. Wound healing in plasma-treated animals slowed down after the course had been completed. Overall, the results show considerable potential for non-thermal argon plasma in eliminating pathogenic bacteria from biofilms and wound surfaces.Abbreviation: CI, confidence interval.

Dielectric Barrier Discharge Atmospheric Cold Plasma for Inactivation of Pseudomonas aeruginosa Biofilms

“…For SEM analysis, untreated controls and P. aeruginosa biofilms treated directly or indirectly with ACP for 300 s were selected and prepared as described by Gratao et al, 30 with minor modifications. The cells were fixed in ice-cold 2.5% glutaraldehyde in 0.05 M sodium cacodylate buffer (pH 7.4) (SCB) for 2 h. The cells were washed with the same buffer three times and were then fixed in 1% osmium tetroxide for 2 h at 4°C.…”

Combination of Cold Atmospheric Plasma and Vitamin C Effectively Disrupts Bacterial Biofilms

“…Three to five-day course of cold plasma treatment has been shown to be required in order to reduce the bacterial load (Psudomonas aeruginosa) on the wounds [14]. It has been established that, once the plasma treatment course is stopped, wound-healing also slows down [14]. Another in vivo study, using a Micro Plaster alpha device also suggests that wound healing may be accelerated by the CAP treatment [15].…”

“…CAP not only enhances the wound healing process but also contains the spread of multi-drug resistant bacteria [13]. Three to five-day course of cold plasma treatment has been shown to be required in order to reduce the bacterial load (Psudomonas aeruginosa) on the wounds [14]. It has been established that, once the plasma treatment course is stopped, wound-healing also slows down [14].…”

Terminal sterilization: Conventional methods versus emerging cold atmospheric pressure plasma technology for non‐viable biological tissues

“…[89] These nontoxic gases become germicidal only after the plasma is ignited, since they are not biocidal on their own. [90] Concentration of produced plasma agents (i.e.…”

“…[112] Less resistant vegetative bacteria have also been tested against the antimicrobial activity of CAP, and were eliminated with different degrees of survival, including gramnegative: Escherichia coli [111,113,114] , Salmonella typhimuriu [115] , and gram-positive Staphylocuccus epidermidis [90,113,116] , Staphylococcus aureus [90,114] , Micrococcus luteus [95] , Streptococcus pyogenes [90] , Enterococcus faecalis [117] and Enterococcus faecium. [90] Gramnegative bacteria are more susceptible to gas plasma treatments than gram-positive [104,118] and differences in susceptibility are thought to be due to variation in the thickness of the peptidoglycan murein layer in the bacterial cell wall. [86,104] Skin floral bacteria Staphylococcus epidermidis is of particular importance in sterilization of TBTM given its frequent association with contamination from procurement and processing sites.…”