[Inactivation of Candida species using cold atmospheric plasma on the way to a new method of eradication of superficial fungal infections].

Introduction: In recent years, nosocomial fungal infections are becoming an increasingly serious problem. More and more complications are observed in patients with high-risk groups resulting from the colonization of the skin and mucous membranes by Candida species. Thus, rapid and effective treatment of superficial fungal infections caused by Candida is a very important task for modern medicine. Unfortunately, with a clear increase in the number of fungal infections, the resistance to currently used antifungal drugs also increases seriously limited the effectiveness of treatment. An intensive search for new therapeutic solutions is therefore necessary. One of the promising solutions is the use of cold atmospheric plasma. The aim of this paper is to investigate the influence of this type of plasma on survival of Candida albicans.

Methods: As a source of cold atmospheric plasma, a linear microdischarge jet, called plasma razor, was used. Plasma was generated at 13.56 MHz, using He as a reactive gas. The gas flow rate and the discharge power were 1.9 L/min and 17 W, respectively. A schematic view of the experimental system is shown in Fig. 1. The reference strain of Candida albicans ATCC 10231 was used as a model material for investigations. The culture was prepared by spreading uniformly 100 μL phosphate buffered saline solution containing 5 x10(7) cells/mL on the surface of a Petri dish. Such a culture was exposed to the plasma at various times. The size of the zone of inhibition of fungal growth was estimated by densitometric method (Fig. 3). For more complete information about the plasma the optical emission spectra were measured.

Results: It was found that with increasing time of plasma treatment, the zone of inhibition clearly increases (Fig. 2). In Fig. 4, the experimental results of the size of the inhibition zone versus the treatment time are shown. These results were successfully fitted (p = 0.0058, r2 = 0.944) by a theoretical curve (Fig. 4), plotted according to Eq. (5), which was derived on the basis of a simple model of the spread of a killing agent from the plasma center. The study of the optical emission spectra confirmed a large variety of possible killing agents generated in the cold atmospheric plasma, such as UV, radicals, ions and energetic electrons. Further research will be focused on the determination of the main agent responsible for the process of the cell killing, and to determine the mechanism of this process.

Conclusions: Cold atmospheric plasma generated by the plasma razor turns out to be a very effective tool for the killing of pathogenic fungi. Although the presented studies are only the initial stage of work on the effects of cold atmospheric microplasma on fungal cells, they provide hope for the possibility of using this technique as a method of eradication of superficial fungal infections.