Influence of the Air Humidity on the Reduction of Bacillus Spores in a Defined Environment at Atmospheric Pressure Using a Dielectric Barrier Surface Discharge

Abstract

From literature different plasma species are known for their possibility to inactivate microorganisms. Most studies report on the inactivation of germs by UV light emitted from rare gas discharges like plasma‐jets or low pressure discharges or disruption of cell membranes due to charging effects. Our aim was to show the influence of air humidity and active plasma power in a simple atmospheric pressure dielectric barrier surface discharge on the reduction of Bacillus atrophaeus spores within a few minutes of treatment time. The plasma treatment time was varied at humidity levels between 0 and 70% relative moisture with a distance of 0.6 mm between the dielectric barrier and test strip. The obtained results have shown an influence of the air humidity on the spore inactivation rate which has been reached by plasma treatment. The plasma does not emit a significant amount of UV light below 320 nm. From these results the role of reactive species, especially the effect of hydroxyl radicals, is discussed.

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“…This can filter out the effects of some ROS/RNS, since their concentrations at the cell/tissue location may fall below the threshold of their biological effects. For example, current evidence of bacterial inactivation studies suggests that UV photons play a less important role than ROS [92]- [94]. Figure 2 shows a damaged membrane of B. subtilis spores after plasma treatment, typical of a result of oxidation.…”

Low temperature atmospheric pressure plasma sources for microbial decontamination

“…This is a reduction factor of 4 log 10 for 10 5 CFU/ml initial concentration after 150 s ‡ In this review the unit of the gas flow rate is generally denoted as it is done in the accordant reference. (Hähnel et al, 2010b;Oehmigen et al, 2010) plasma treatment. Additional pulse length variations indicate an exponential correlation between the plasma on-time and reduction rate.…”

“…Within 10 min of treatment time almost all bacteria in dry or wet environment could be reduced about 5 log 10 . Hähnel et al (2010b) used the remote impact of a surface DBD in ambient air for inactivation of microorganisms (figure 6a). Therefore, a special electrode geometry based on that shown in figure 4e was invented.…”

Inactivation of Bacteria by Non-Thermal Plasmas

“…Heise et al (Heise et al, 2004) observed that the spore reduction of B. subtilis depends on which working gas is used to sustain the DBD: the efficiency of the discharge is the lowest when air is employed and the highest with argon as discharge gas. More recently, Hähnel et al (Hahnel et al, 2010) observed that air humidity in a dielectric barrier surface discharge has a significant influence on the bacterial inactivation rate: higher concentration of water vapour in the process gas leads to higher killing rates of micro-organisms. To enable the internal sterilization of complicated medical instruments, such as breathing circuits, catheders and endoscopes, different authors have developed special DBD configurations (Eto et al, 2008, Pointu et al, 2008, Sato et al, 2008.…”

“…These authors found that besides direct exposure, also remote plasma treatment can achieve effective bacterial inactivation . Besides DBDs in the homogeneous mode, also filamentary discharges have been employed for the sterilization of various bacteria (Kostov et al, 2010, Heise et al, 2004, Trompeter et al, 2002, Hahnel et al, 2010, Yasuda et al, 2008. Kostov et al (Kostov et al, 2010) and Yasuda et al (Yasuda et al, 2008) were able to achieve sterilization of E. coli with their filamentary air DBD, while Trompeter et al (Trompeter et al, 2002) focussed on the inactivation of B. subtilis and Aspergillus Niger with DBDs sustained in different working gases.…”