Evidence of Temporal Postdischarge Decontamination of Bacteria by Gliding Electric Discharges: Application to Hafnia alvei

This study aimed to characterize the bacterium-destroying properties of a gliding arc plasma device duringelectric discharges and also under temporal postdischarge conditions (i.e., when the discharge was switchedoff). This phenomenon was reported for the first time in the literature in the case of the plasma destruction ofmicroorganisms. When cells of a model bacterium, Hafnia alvei, were exposed to electric discharges, followedor not followed by temporal postdischarges, the survival curves exhibited a shoulder and then log-linear decay.These destruction kinetics were modeled using GinaFiT, a freeware tool to assess microbial survival curves,and adjustment parameters were determined. The efficiency of postdischarge treatments was clearly affected bythe discharge time (t*); both the shoulder length and the inactivation rate kmax were linearly modified as afunction of t*. Nevertheless, all conditions tested (t* ranging from 2 to 5 min) made it possible to achieve anabatement of at least 7 decimal logarithm units. Postdischarge treatment was also efficient against bacteria notsubjected to direct discharge, and the disinfecting properties of “plasma-activated water” were dependent onthe treatment time for the solution. Water treated with plasma for 2 min achieved a 3.7-decimal-logarithm-unitreduction in 20 min after application to cells, and abatement greater than 7 decimal logarithm units resultedfrom the same contact time with water activated with plasma for 10 min. These disinfecting properties weremaintained during storage of activated water for 30 min. After that, they declined as the storage time increased.