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 Gram-negative bacteriaPseudomonas aeruginosa,Burkholderia cenocepaciaandEscherichia coli, there were no survivors among the initial 105c.f.u. after a 5 min plasma treatment. The susceptibility of Gram-positive bacteria was species- and strain-specific.Streptococcus pyogeneswas the most resistant with 17 % survival of the initial 105c.f.u. after a 5 min plasma treatment.Staphylococcus aureushad a strain-dependent resistance with 0 and 10 % survival from 105c.f.u. of the Sa 78 and ATCC 6538 strains, respectively.Staphylococcus epidermidisandEnterococcus faeciumhad 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 withP. aeruginosaand the plasma-sensitiveStaphylococcus aureusstrain 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 eliminatedP. aeruginosafrom 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.