Antibacterial efficacy of cold atmospheric plasma against Enterococcus faecalis planktonic cultures and biofilms in vitro

Abstract

Nosocomial infections have become a serious threat in our times and are getting more difficult to handle due to increasing development of resistances in bacteria. In this light, cold atmospheric plasma (CAP), which is known to effectively inactivate microorganisms, may be a promising alternative for application in the fields of dentistry and dermatology. CAPs are partly ionised gases, which operate at low temperature and are composed of electrons, ions, excited atoms and molecules, reactive oxygen and nitrogen species. In this study, the effect of CAP generated from ambient air was investigated against Enterococcus faecalis, grown on agar plates or as biofilms cultured for up to 72 h. CAP reduced the colony forming units (CFU) on agar plates by > 7 log10 steps. Treatment of 24 h old biofilms of E. faecalis resulted in CFU-reductions by ≥ 3 log10 steps after CAP treatment for 5 min and by ≥ 5 log10 steps after CAP treatment for 10 min. In biofilm experiments, chlorhexidine (CHX) and UVC radiation served as positive controls and were only slightly more effective than CAP. There was no damage of cytoplasmic membranes upon CAP treatment as shown by spectrometric measurements for release of nucleic acids. Thus, membrane damage seems not to be the primary mechanism of action for CAP towards E. faecalis. Overall, CAP showed pronounced antimicrobial efficacy against E. faecalis on agar plates as well as in biofilms similar to positive controls CHX or UVC.

The Antimicrobial Effect of Cold Atmospheric Plasma against Dental Pathogens—A Systematic Review of In-Vitro Studies

“…The reduction values for devices utilizing ambient air in all time intervals were demonstrated by two of the studies. The application of 60 s led to results ranging from no reduction to 7.9 log 10 reduction units [ 55 ]. For pure helium plasma, outcomes ranged from no reduction [ 45 ] to no detection of CFU within 60 s [ 42 ].…”

“…Lower concentrations of S. mutans and L. acidophilus resulted in an increased inactivation [ 21 , 28 , 32 ]. In general, biofilm maturation was associated with an augmented resistance to CAP application in Gram-positive [ 22 , 24 , 31 , 55 ] and Gram-negative species [ 31 ]. The maturation of the biofilm is accompanied with the production of an extracellular matrix and an increase of biofilm thickness.…”

Safety and bactericidal efficacy of cold atmospheric plasma generated by a flexible surface Dielectric Barrier Discharge device against Pseudomonas aeruginosa in vitro and in vivo

“…This suggests that wound environmental factors such as biofilm formation and wound exudate could have played a role in the limited efficacy of CAP in vivo. It was shown that bacteria in biofilms can be more tolerant against CAP [ 43 – 45 ]. Additionally, bacterial colonization and wound exudate could increase pH and/or introduce buffering effects to the wounds [ 46 ].…”

Development of Antimicrobial Phototreatment Tolerance: Why the Methodology Matters

“…Cold atmospheric plasma (CAP) is a partly ionized gas containing free radicals, ions, electrons and photons which are produced due to the electric field action [ 50 , 51 ]. Due to the light component (photons) it may be considered light-based therapy.…”

“…The principal mecha-nisms of CAP involve cell membrane permeabilization, activity of reactive oxygen and ni-trogen species as well as the chemical reactions leading to DNA damage [ 54 ]. CAP was demonstrated to be an efficient bactericidal treatment leading to Bacillus subtilis and Clos-tridium difficile spores inactivation [ 55 ], eradication of MRSA and E. coli in in vitro porcine skin model [ 56 ], as well as inactivation of other Gram-positive and Gram-negative species [ 51 , 53 , 57 ]. A study aimed at investigating the development of CAP tolerance was described by Matthes et al, employing S. aureus biofilm culture in medium to mimic an artificial wound environment.…”