Plasma Assisted Decontamination of Bacterial Spores

Abstract

The efficacy and mechanism of killing bacterial spores by a plasma torch is studied. Bacterial-spore (Bacillus cereus) suspension is inoculated onto glass/paper slide-coupons and desiccated into dry samples, and inoculated into well-microplate as wet sample. The exposure distance of all samples is 4 cm from the nozzle of the torch. In the experiment, paper slide-coupon is inserted inside an envelope. The kill times on spores in three types of samples are measured to be about 3, 9, and 24 seconds. The changes in the morphology and shape of still viable spores in treated wet samples are recorded by scanning electron and atomic force microscopes. The loss of appendages and exosporium in the structure and squashed/flattened cell shape are observed. The emission spectroscopy of the torch indicates that the plasma effluent carries abundant reactive atomic oxygen, which is responsible for the destruction of spores.

An investigation of inactivation mechanisms of Bacillus amyloliquefaciens spores in non‐thermal plasma of ambient air

“…The presence of water appeared to enhance the efficacy of the NTP‐AA treatment, although another study reported that it was much slower to kill wet spores suspended in water than dry ones on a glass slide with a microwave‐powered air NTP torch because excessive water formed a barrier preventing reactive oxygen species from reaching the spores . No survival was observed for NTP‐treated wet samples of BA spores by plating on nutrient media at even the shortest NTP treatment time of 1 min (Fig.…”

“…Many factors affect the mechanisms of spore inactivation by NTP, even within a narrower domain of non‐thermal atmospheric pressure plasma, making pinpointing the inactivation mechanisms difficult and sometimes controversial. In a study using microwave‐powered air NTP torch, fast inactivation rate (6‐log 10 reduction in ∼17 s) of Bacillus cereus spores was reported, and the NTP torch was able to kill spores inside an paper envelope at a slower rate without damaging the envelope. Effective inactivation of Bacillus spores using atmospheric DBD plasma was also reported .…”

“…Effective inactivation of Bacillus spores using atmospheric DBD plasma was also reported. 55 Of note, the former study 6 observed changes in spore shape and morphological structures and the loss of spore appendages and exosporium after NTP treatment, whereas the later study 55 observed no damage to the spore coats, nor any morphological difference after NTP treatment, and thus the diffusion of chemically active oxygen species into spores followed by the damage of internal macromolecules or molecular systems might be the primary mechanism of spore inactivation. Combining morphological observation and chemical analysis in the present study, we clearly demonstrated that the NTP-AA significantly caused both morphological damage and internal chemical alterations in spores.…”

“…Non-thermal methods can also be used to protect the nation's food supply from intentional contamination and attacks from bio-weapons, such as spores of Bacillus anthracis (the causative agent of 'Anthrax'). [4][5][6] Non-thermal plasma (NTP) is emerging as a leading non-thermal technology for efficiently inactivating microorganisms in various sterilization and food-related applications, at the same time as also being environmentally-friendly, residue-free, dry and rapid. 7 Various forms of NTP can be generated by the application of different energy sources (thermal, electric, magnetic, radiofrequency, microwave, laser, etc.)…”

Innovative research of plasma physics for life sciences

“…Through the oxidation process, chemically reactive oxygen species (ROS) are known to be effective in the disruption of the bacterial cell wall [11][12][13]. The role of oxygen radicals in plasma sterilization has been also demonstrated: the rate of bacterial inactivation in the oxygen plasma group was greater than that in the helium plasma group.…”