1947-5764/17/$35.00 © 2017 by Begell House, Inc. www.begellhouse.com 187 Plasma Medicine, 7(3):187–200 (2017) Ba c te ric id a l Effe c t o f a Die le c tric Ba rrie r Disc ha rg e Pla sm a Je t G e ne ra te d in La m ina r a nd Pre turb ule nt He lium Flo ws Olga Stepanova, a,* Oksana Rybalchenko, a Mikhail Pinchuk, b Alexander $VWDｿHY a Olga Orlova, a Valentin Spodobin, b & Anatoly Kudryavtsev a a Saint Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg, 199034, Russia; b Institute for Electrophysics and Electric Power of Russian Academy of Sciences, 18 Dvortsovaya nab., St. Petersburg, 191186, Russia *Address all correspondence to: Olga Stepanova, St. Petersburg State University, 8a 21st line of Vasilyevsky Island, St. Petersburg, 199106, Russia; Tel.: +7(812)3260326; Fax: +7(812)3292473, E-mail: o.m.stepanova@spbu.ru ABSTRACT: The bactericidal effect of a helium dielectric barrier discharge plasma jet gen- HUDWHG LQ ODPLQDU DW  PV DQG SUHWXUEXOHQW DW  PV KHOLXP ﾀRZV LV FRQVLGHUHG LQ WHUPV of average discharge power and distance of treatment of Escherichia coli cells grown on a nutrient agar surface in a Petri dish. Sizes of bacteria inhibition zones are estimated and mor- phological changes in ultrastructure of bacterial cells are revealed using electron microscopy. 7KLV VWXG\ VXJJHVWV WKDW WKH JDV ﾀRZ UHJLPH LV DQ LPSRUWDQW IDFWRU LQ WKH SURGXFWLRQ RI WKH helium plasma jet used to inhibit bacteria. We reveal the different responses of E. coli cells WUHDWHG E\ WKH KHOLXP SODVPD MHW JHQHUDWHG LQ ODPLQDU DQG SUHWXUEXOHQW JDV ﾀRZV 1XPHURXV IRFDO GHVWUXFWLRQV DSSHDU LQ WKH FHOOV DIWHU  PLQ RI WUHDWPHQW ZLWK WKH ODPLQDU JDV ﾀRZ UHJLPH Along with these focal destructions, expansion of cytoplasm and a superhelix of nucleoids are revealed with the preturbulent regime. We explain differences in behavior of cell morphology XQGHU WKH SODVPD MHW IRUPHG DW GLIIHUHQW JDV ﾀRZ UHJLPHV E\ WKH GLIIHUHQW JDVG\QDPLF FRQGL- WLRQV RI PL[LQJ DPELHQW DLU LQWR WKH KHOLXP ﾀRZ KEY WORDS: GLHOHFWULF EDUULHU GLVFKDUJH KHOLXP SODVPD MHW ODPLQDU JDV ﾀRZ SUHWXUEXOHQW JDV ﾀRZ EDFWHULFLGDO HIIHFW PRUSKRORJLFDO SURSHUWLHV HOHFWURQ PLFURVFRS\ I. INTRO DUC TIO N 3ODVPD MHW JHQHUDWRUV EDVHG RQ GLHOHFWULF EDUULHU GLVFKDUJH '%' DUH FODVVLｿHG DV D type of low-temperature (strongly nonequilibrium) plasma source that can operate at atmospheric pressure. Such generators can be used in laboratory and clinical investiga- WLRQV WKDW DUH DLPHG DW H[DPLQLQJ EDFWHULFLGDO HIｿFDF\ RI ORZWHPSHUDWXUH DWPRVSKHULF pressure plasma and developing ways to enhance it. 1–4 The generators usually produce SODVPD MHWV DIWHU D JDV ﾀRZ SDVVHV WKURXJK D F\OLQGULFDO GLVFKDUJH FHOO PDGH RI GLHOHFWULF material, inside which the DBD is ignited. 5–9 Inert gases (helium in particular) are often used to create a cold atmospheric plasma jet. Typical parameters of alternating current voltage supply for helium are as follow: pulse repetition frequency in tens of kilohertz and voltage amplitude in kilovolts. 7–9 The helium plasma jet propagates from the nozzle of the generator into the surrounding air. The formation of the plasma jet at the outlet of the generator depends on a number of factors including gas outlet velocity, 10 impurity FRPSRVLWLRQ RI D WRWDO JDV ﾀRZ 11 and peak-to-peak value of discharge voltage. 12