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INTRODUCTION. The use of plasma for sanitization purpose is of increasing interest. Annular plasma synthetic jet actuators (PSJAs) had demonstrated their ability to produce and induced tubular flow (Neretti et al., 2017, J. Phys. D: Appl. Phys. 50 015210, 9pp) normal to the surface where the dielectric barrier discharge is ignited. This typology of reactor enhances the transport of reactive species toward the treated samples (Taglioli et al., 2016, Plasma sources Sci. Technol., 25 06LT01-5pp.). Long life charged particles are generated within the plasma region and then can be advected together with the induced flow. In this work the effect of free charges into induced flow have been tested against Candida guilliermondii both in agar plates and in water suspension. MATERIALS AND METHODS. Eighty ml suspension of C. guiliiermondii in saline solution (0.5 Mcfarland opacity) was prepared. The CFU of untreated suspension was determined performing multiple dilution that were plated on Sabouraud Dextrose Agar (SDA) petri dishes that were incubated at 26°C for 48 hours. Aliquots of 100 μl of suspension were spread on the surface of 6 SDA plates (9 cm diameter); aliquots of 20 ml of suspension were put into six 9 cm plates. Agar plates were subjected to induced flow for 30 sec, 2 and 5 minutes and suspension plates for 5, 10 and 15 minutes, both with and without blocking the charges by a grounded metallic mesh. After treating, from each suspension CFU was calculated as previous described, while in the agar plates the colonies were directly counted after incubation. RESULTS AND CONCLUSIONS. The untreated yeast suspension contained 5.21 x 105 CFU/100 μl. In treated samples, the reduction of the CFU of the yeast was related to the treatment time and to presence/absence of free charges. The effect was greater on agar plate than on suspension: at the same time of treatment (5 minutes), only 1-log reduction of CFU were observed on suspension, while 4-log reduction was observed in agar plates. Additional 1-log reduction was observed when free charges have been allowed to reach the sample. On suspension, longer treatment time (15 min) was needed to obtain 2-log reduction without free charges and 4-log reduction with free charges. |
