Sporicidal Action of Pulsed Radiation of Hot Plasma

Nitration is one of the main reaction mechanisms of long-living reactive species (oxygen and nitrogen products) formed under the action of pulsed radiation of hot plasma. The long lifetime of reactive species formed in a discharge zone (up to several days) enables them to penetrate deep into the objects covered with a protective coat. Spores are such objects.

The aim of the investigation was to study sporicidal activity of hot plasma pulsed radiation of spark electric discharge by the analysis findings of active products formed in an aqueous L-tyrosine solution under the effect of the discharge.

Materials and Methods. In the study, we used a Pilimin IR-10 spark discharge generator as a source of pulsed radiation of hot plasma; a corona discharge generator — as a source of cold plasma; a DKB-9 low-pressure mercury lamp — as a source of continuous radiation of UV band, wavelength of 253.7 nm. The samples were processed in Petri dishes, 40 mm in diameter, their volume being 4 and 10 cm³. The study used an L-tyrosine solution in distilled water (the concentration: 160 mg/L), a suspension of bacteria and spores of micromycetes (its concentration being ~10⁶ cells per 1 ml). Tyrosine conversion products were identified spectrophotometrically before and after treatment. The biocidal and sporicidal effects were assessed by counting CFU (colony-forming units) after seeding incubation at 27–37°C.

Results. The oxidation of tyrosine by HO₂^• radicals was found to be impossible. Under the action of nitrogen compounds, nitration proceeds with 3-nitrotyrosine formation. The nitration reaction is slow, taking about 100 h. A possible nitration mechanism is through the formation of the nitronium ion NO₂⁺ in an acidic medium.

The biocidal effect of hot plasma radiation turned out to be weaker than that of UV radiation of a DKB-9 lamp. This is due to the difference in their emission spectrum. The sporicidal effect of hot plasma radiation was more pronounced: a 10-fold decrease in the number of CFU was observed at radiation doses of 200–280 J. Under the action of UV radiation, at the same doses, the decrease in the number of CFU was from 3 to ~30%. The sporicidal effect of hot plasma radiation is due to the decay of a long-living …ONOOH/ONOO^–… complex with the formation of a nitric oxide and a nitronium ion in an acidic medium.

Conclusion. The study showed the viability of spores under the action of pulsed radiation of hot plasma to decrease. While the light radiation of a UV lamp, under studied conditions, slightly penetrates the protective coating of a spore. The sporicidal effect of hot plasma radiation is due to the decay of a long-living …ONOOH/ONOO^–… complex with the formation of a nitric oxide and a nitronium ion in an acidic medium. Nitration plays a decisive role in the sporicidal action of the hot plasma radiation of a spark discharge. The principle of the sporicidal effect of gas-discharge plasma radiation can be used to develop disinfecting devices.

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Piskarev I.M., Ivanova I.P. Sporicidal Action of Pulsed Radiation of Hot Plasma. Sovremennye tehnologii v medicine 2022; 14(4): 17, https://doi.org/10.17691/stm2022.14.4.02