Plasma Medicine in Dermatology: Basic Antimicrobial Efficacy Testing as Prerequisite to Clinical Plasma Therapy

Plasma medicine has become an emerging field in medical sciences since cold plasma has demonstrated significant antibacterial properties in vitro and in vivo. However, systematic antimicrobial plasma testing against bacteria, fungi, and parasites is still lacking. Chronic wounds, fungal skin and nail infections, and colonization with multidrug-resistant pathogens like Staphylococcus aureus (MRSA) often pose significant therapeutic and economical problems and new therapeutic concepts are strongly warranted. The challenge of worldwide increasing resistance problems including different pathogens like methicillin-resistant MRSA, vancomycin-resistant enterococci, and gram-negative species producing betalactam hydrolysing enzymes (extended spectrum ß-lactamases) constitute the need for alternative antimicrobial treatments. Cold plasma therapy with a completely different mode of action compared to conventional antimicrobials may offer an alternative to conventional external antibiotic and antiseptic therapies. In order to estimate the possible role as physical antiseptic, basic susceptibility data from plasma are needed. To provide such data, the plasma susceptibility of representative skin and wound pathogens against low-temperature atmospheric pressure plasma jet (APPJ device) and dielectric barrier discharge plasma treatment was tested in vitro on agar. The same plasma sources were used to test clinical fungal isolates in vitro and isolates of the parasite demodex folliculorum ex vivo. Plasma treatment proved to be highly effective in eradicating all treated strains and species including Escherichia coli, Pseudomonas aeruginosa, Klebsiella group (K. pneumoniae ssp. pneumoniae, K. oxytoca), Staphylococcus aureus, hemolysing Lancefield Streptococci (group A and B), Proteus group (P. mirabilis, P. vulgaris), Acinetobacter spp., Stenotrophomonas spp., Enterococcus faecalis, Candida albicans, and Staphylococcus epidermidis. Plasma irradiation of Trichophyton rubrum, Trichophyton interdigitale, Microsporon canis, and the yeast Candida albicans was able to kill >90% of the organisms during 30 s in vitro with no isolate exhibiting resistance. The APPJ-plasma killed Demodex folliculorum after exposure time of 2 s. Our data suggest plasma as a possible new option in the treatment of microbial, fungal, and parasitic dermal infections.