Modification of bacterial structures by a low‐temperature gas plasma and influence on packaging material

Aims: To investigate the effect of a cascaded dielectric barrier discharge (CDBD) treatment on the biological structure of a selected bacterium and on the properties of different polymer films. Methods and Results: Inactivation kinetics were measured using air as the process gas and using Bacillus atrophaeus spores and vegetative cells, which had been homogeneously distributed on a surface. The changes to the outer coats and the DNA of the endospores and cells after plasma treatment were determined using biomolecular and chemical methods. The experiments showed that damage to the DNA molecules and changes in the cell walls can be observed as a consequence of the CDBD treatment. Furthermore, the influence of the plasma treatment on the properties of various polymer films was investigated using a variety of test methods. Except the sealing strength where a slight decrease was observed (max. 20%), no negative changes of the material properties have occurred. Conclusions: CDBD treatment can affect the DNA of spores and cells, depending on the treatment time. At the same time, practically relevant inactivation rates on packaging materials were observed, without any significant changes to the material properties. Significance and Impact of the Study: Knowledge about CDBD mechanisms was acquired from a biological point of view, and the suitability of the method for treating polymer films was demonstrated.     

Sterilization efficiency of a cascaded dielectric barrier discharge

AIMS: To investigate the microbial inactivation efficiency of a newly developed cascaded dielectric barrier discharge (CDBD) set-up against various micro-organisms on polyethylene terephthalate (PET) foils. METHODS AND RESULTS: Inactivation kinetics in dependency of time were produced with air as process gas and test strains like Salmonella serotype Mons, Staphylococcus aureus and Escherichia coli and spores of Bacillus atrophaeus, Aspergillus niger and Clostridium botulinum, which were homogeneously distributed on the sample surface by a spray method. Highest count reduction was observed for the vegetative cells with at least 6.6 log(10) within 1 s. Aspergillus niger was the most resistant test strain with an inactivation rate of about 5 log(10) in 5 s. CONCLUSIONS: For industrial applications it is necessary to evaluate new sterilization methods against a broad range of different micro-organisms. SIGNIFICANCE AND IMPACT OF THE STUDY: CDBD plasma is a fast and effective technology for decontamination of heat sensitive materials in few seconds.     

三种选育高乙醇耐受性工业酿酒酵母方法的比较

由于乙醇耐性受多基因控制,因此需要从全基因组水平进行改造以期得到高乙醇耐受的突变体。文中分别使用紫外诱变、等离子体诱变及人工转录因子3种方法对工业酿酒酵母Sc4126进行改造,获得了乙醇耐性提高的突变体,并比较了3种方法的正突变率。人工转录因子文库转化的方法获得了最多数量的乙醇耐性突变体,高出紫外诱变和等离子体诱变方法1~2个数量级,且遗传稳定。研究结果表明,人工转录因子技术可以用于对工业酿酒酵母快速进行基因组工程改造。     

Lethal effect of the gliding arc discharges on Erwinia spp

AIMS: To compare the decontamination performances of glidarc on strains of Erwinia of industrial interest. METHODS AND RESULTS: Cultures of Erwinia carotovora carotovora, Erwinia carotovora atroseptica and Erwinia chrysanthemi taken in stationary phase were exposed to the plasma generated by electric discharges in a gliding arc reactor prototype. The kinetics of destruction of bacteria were followed by direct platting. All bacterial strains presented a three-phase destruction kinetics leading to an apparent sterilization within 10 min. Epifluorescent observations using life/dead probes revealed the absence of viable but not cultivable resistant forms. Measurement of the physical parameters of the medium confirmed that the technique was nonthermal but that reactive species responsible for a decrease of the pH were generated. However, even after neutralization the medium did not allow bacterial growth. CONCLUSIONS: The results demonstrate that glidarc allows a rapid and complete destruction of planctonic strains of Erwinias without formation of resistant forms. SIGNIFICANCE AND IMPACT OF THE STUDY: The reduction rate obtained by this technique shows the great industrial interest of glidarc for decontamination and suggests that it can be used for sterilization of industrial water effluents.     

Plasma-induced dimerization of phloridzin as a new class of anti-adipogenic agents

Phloridzin is a natural phloretin glucoside found in several parts of apple trees and is an attractive target for structural modification as novel pharmaceutical agent. Nonthermal dielectric barrier discharge (DBD) plasma-induced structural changes in dihydrochalcone phloridzin (1) resulted in the isolation of three new methylene-bridged dihydrochalcone dimers, methylenebisphloridzin (2), deglucosylmethylenebisphloridzin (3), and methylenebisphloretin (4), along with phloretin (5). The chemical structures of these newly generated compounds were elucidated by interpretation of their spectroscopic data. The new phloretin dimer 4 connected by a methylene linkage exhibited significantly improved anti-adipogenic properties against pancreatic lipase as well as differentiation of 3T3-L1 preadipocytes compared to the parent compound phloridzin.     

Incorporating germination‐induction into decontamination strategies for bacterial spores

Oenococcus oeni is the dominant species able to cope with a hostile environment of wines, comprising cumulative effects of low pH, high ethanol and SO₂ content, nonoptimal growth temperatures and growth inhibitory compounds. Ethanol tolerance is a crucial feature for the activity of O. oeni cells in wine because ethanol acts as a disordering agent of its cell membrane and negatively affects metabolic activity; it damages the membrane integrity, decreases cell viability and, as other stress conditions, delays the start of malolactic fermentation with a consequent alteration of wine quality. The cell wall, cytoplasmic membrane and metabolic pathways are the main sites involved in physiological changes aimed to ensure an adequate adaptive response to ethanol stress and to face the oxidative damage caused by increasing production of reactive oxygen species. Improving our understanding of the cellular impact of ethanol toxicity and how the cell responds to ethanol stress can facilitate the development of strategies to enhance microbial ethanol tolerance; this allows to perform a multidisciplinary endeavour requiring not only an ecological study of the spontaneous process but also the characterization of useful technological and physiological features of the predominant strains in order to select those with the highest potential for industrial applications.     

不同处理条件对介质阻挡放电低温等离子体杀菌效果及影响机理研究

【目的】研究不同处理条件下介质阻挡放电低温等离子体对单增李斯特菌和肠炎沙门氏菌的杀菌效果,以及抑菌活性物质含量随处理时间的变化。【方法】以单增李斯特菌和肠炎沙门氏菌为对象,研究不同电压、时间及氧气浓度对介质阻挡放电低温等离子体杀菌效果的影响,通过气态活性物质测定管测定O₃和NO₂浓度随处理时间的变化,利用荧光强度表征菌液中产生的活性物质浓度,采用荧光分光光度法测定·OH、H₂O₂和¹O₂随处理时间的变化。【结果】采用70 kV、150 s或80 kV、1₂0 s能够完全杀灭肠炎沙门氏菌,而单增李斯特菌只在80kV、1₂0s条件下才能被完全杀死。采用50%O₂+50%N₂的混合气体能够在90 s内完全杀死细菌。随处理时间的增加,两种菌体细胞内活性氧物质含量呈逐渐增加趋势。【结论】电压、时间及氧气浓度均能显著增强等离子体的杀菌效果,其杀菌作用主要与H₂O₂、·OH、1O₂等活性氧物质的含量有关,其中·OH和H₂O₂是介质阻挡放电等离子体杀菌的主要物质。     

Factors affecting the inactivation of micro-organisms by intense light pulses

AIM: To determine the influence of several factors on the inactivation of micro-organisms by intense light pulses (ILP). METHODS AND RESULTS: Micro-organisms on agar media were flashed 50 times under different conditions and their inactivation measured. Micro-organisms differed in sensitivity to ILP but no pattern was observed among different groups. Several enumeration methods to quantify the effect of ILP were investigated and showed relevant differences, shading effect and photoreactivation accounted for them, the strike method yielded the most reliable results. Higher decontamination efficiencies were obtained for Petri dishes located close to the strobe and inside the illumination cone. Decontamination efficacy decreased significantly at contamination levels >6.85 log(10). After 13 successive treatments, no resistance to ILP could be demonstrated. Media warming up depended on the distance from the strobe and the number of flashes. CONCLUSIONS: For an industrial implementation: the position and orientation of strobes in an unit will determine the lethality, products should be flashed as soon as possible after contamination occurs, a cooling system should be used for heat-sensitive products and flashed products should be light protected. No resistant flora is expected to develop. SIGNIFICANCE AND IMPACT OF THE STUDY: Conclusions derived from this work will allow a better implementation of this decontamination technique at industrial level.