OBJECTIVETo investigate the effect of low-temperature plasma on inactivation of bacterial spores and explore the mechanism.

METHODSDielectric barrier discharge (DBD) was employed to generate the atmospheric low-temperature plasma for treatment of B.subtilis var. niger spores with the gas spacing of 3, 4 and 5 and treatment time intervals of 5, 10, 15, 20, 25, 30 and 35 s. The survived colonies was counted with plate counting method, and the killing log value (KLV) at different treatment times was calculated. The inactivation effect of electric field on B.subtilis var.niger spores was also investigated and the spores treated with low-temperature plasma were observed with transmission electron microscope.

RESULTSWith the gap spacing of 3, 4 and 5 mm, the KLV of low-temperature plasma on B.subtilis var.niger spores within 25, 30 and 35 s of exposure was more than 5. The germicidal effects of the electric field on B. subtilis var.niger spores were rather poor. Transmission electron microscopy demonstrated total destruction of the surface and interior structure of the spores by low-temperature plasma.

CONCLUSIONSLow-temperature plasma is effective for inactivation of the bacterial spores with a time and dose dependence. The penetrating effect of charged particles and oxygenation effect of the reactive oxygen species might play a dominant role in plasma-induced bacterial spore inactivation, while the role of electric field is negligible.

Bacillus subtilis ; growth & development ; Cold Temperature ; Microbial Viability ; Plasma Gases ; pharmacology ; Spores, Bacterial ; growth & development ; Sterilization ; methods

Escherichia coli AFP111 is a spontaneous mutant with mutations in the glucose specific phosphotransferase system (ptsG) in NZN111 (delta pflAB deltaldhA). In AFP111, conversion of xylose to succinic acid generates 1.67 molecule of ATP per xylose. However, the strain needs 2.67 molecule ATP for xylose metabolism. Therefore, AFP111 cannot use xylose due to insufficient ATP under anaerobic condition. Through an atmospheric and room temperature plasma (ARTP) jet, we got a mutant strain named DC111 that could use xylose under anaerobic condition in M9 medium to produce succinic acid. After 72 h, DC111 consumed 10.52 g/L xylose to produce 6.46 g/L succinic acid, and the yield was 0.78 mol/mol. Furthermore, the reaction catalyzed by the ATP-generating PEP-carboxykinase (PCK) was enhanced. The specific activity of PCK was 19.33-fold higher in DC111 than that in AFP111, which made the strain have enough ATP to converse xylose to succinic acid.
Atmosphere ; Escherichia coli ; genetics ; metabolism ; Fermentation ; Industrial Microbiology ; Metabolic Engineering ; Mutation ; Plasma Gases ; pharmacology ; Succinic Acid ; metabolism ; Temperature ; Xylose ; metabolism

PURPOSE: To determine the effects of nonthermal plasma (NTP) induced by helium (He) alone or He plus oxygen (O2) on the generation of reactive oxygen species (ROS) and cell death in anaplastic thyroid cancer cells. MATERIALS AND METHODS: NTP was generated in He alone or He plus O2 blowing through a nozzle by applying a high alternating current voltage to the discharge electrodes. Optical emission spectroscopy was used to identify various excited plasma species. The apoptotic effect of NTP on the anaplastic thyroid cancer cell lines, such as HTH83, U-HTH 7, and SW1763, was verified with annexin V/propidium staining and TUNEL assay. ROS formation after NTP treatment was identified with fluorescence-activated cell sorting with DCFDA staining. The mitogen-activated protein kinase pathways and caspase cascade were investigated to evaluate the molecular mechanism involved and cellular targets of plasma. RESULTS: NTP induced significant apoptosis in all three cancer cell lines. The plasma using He and O2 generated more O2-related species, and increased apoptosis and intracellular ROS formation compared with the plasma using He alone. NTP treatment of SW1763 increased the expression of phosphor-JNK, phosphor-p38, and caspase-3, but not phosphor-ERK. Apoptosis of SW1763 as well as expressions of elevated phosphor-JNK, phosphor-p38, and caspase-3 induced by NTP were effectively inhibited by intracellular ROS scavengers. CONCLUSION: NTP using He plus O2 induced significant apoptosis in anaplastic cancer cell lines through intracellular ROS formation. This may represent a new promising treatment modality for this highly lethal disease.
Apoptosis/*drug effects ; Caspase 3/*metabolism ; Flow Cytometry ; Humans ; Male ; Plasma Gases/*pharmacology ; Reactive Oxygen Species/*metabolism ; Spectrometry, X-Ray Emission ; Thyroid Carcinoma, Anaplastic ; p38 Mitogen-Activated Protein Kinases/*metabolism