共查询到20条相似文献,搜索用时 78 毫秒
1.
M. W. Ahmed S. Choi K. Lyakhov U. Shaislamov R. K. Mongre D. K. Jeong R. Suresh H. J. Lee 《Plasma Physics Reports》2017,43(3):381-392
Plasma discharge is a novel disinfection and effectual inactivation approach to treat microorganisms in aqueous systems. Inactivation of Gram-negative Escherichia coli (E. coli) by generating high-frequency, high-voltage, oxygen (O2) injected and hydrogen peroxide (H2O2) added discharge in water was achieved. The effect of H2O2 dose and oxygen injection rate on electrical characteristics of discharge and E. coli disinfection has been reported. Microbial log reduction dependent on H2O2 addition with O2 injection was observed. The time variation of the inactivation efficiency quantified by the log reduction of the initial E. coli population on the basis of optical density measurement was reported. The analysis of emission spectrum recorded after discharge occurrence illustrated the formation of oxidant species (OH?, H, and O). Interestingly, the results demonstrated that O2 injected and H2O2 added, underwater plasma discharge had fabulous impact on the E. coli sterilization. The oxygen injection notably reduced the voltage needed for generating breakdown in flowing water and escalated the power of discharge pulses. No impact of hydrogen peroxide addition on breakdown voltage was observed. A significant role of oxidant species in bacterial inactivation also has been identified. Furthermore the E. coli survivability in plasma treated water with oxygen injection and hydrogen peroxide addition drastically reduced to zero. The time course study also showed that the retardant effect on E. coli colony multiplication in plasma treated water was favorable, observed after long time. High-frequency underwater plasma discharge based biological applications is technically relevant and would act as baseline data for the development of novel antibacterial processing strategies. 相似文献
2.
Different Inactivation Behaviors of MS-2 Phage and Escherichia coli in TiO2 Photocatalytic Disinfection 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Despite a wealth of experimental evidence concerning the efficacy of the biocidal action associated with the TiO2 photocatalytic reaction, our understanding of the photochemical mechanism of this particular biocidal action remains largely unclear. It is generally accepted that the hydroxyl radical (·OH), which is generated on the surface of UV-illuminated TiO2, plays the main role. However, our understanding of the exact mode of action of the hydroxyl radical in killing microorganisms is far from complete, and some studies report that other reactive oxygen species (ROS) (H2O2 and O2·−, etc.) also play significant roles. In particular, whether hydroxyl radicals remain bound to the surface or diffuse into the solution bulk is under active debate. In order to examine the exact mode of action of ROS in inactivating the microorganism, we tested and compared the levels of photocatalytic inactivation of MS-2 phage and Escherichia coli as representative species of viruses and bacteria, respectively. To compare photocatalytic microbial inactivation with the photocatalytic chemical degradation reaction, para-chlorobenzoic acid, which rapidly reacts with a hydroxyl radical with a diffusion-limited rate, was used as a probe compound. Two different hydroxyl radical scavengers, tert-butanol and methanol, and an activator of the bulk phase hydroxyl radical generation, Fe2+, were used to investigate their effects on the photocatalytic mode of action of the hydroxyl radical in inactivating the microorganism. The results show that the biocidal modes of action of ROS are very different depending on the specific microorganism involved, although the reason for this is not clear. It seems that MS-2 phage is inactivated mainly by the free hydroxyl radical in the solution bulk but that E. coli is inactivated by both the free and the surface-bound hydroxyl radicals. E. coli might also be inactivated by other ROS, such as O2·− and H2O2, according to the present results. 相似文献
3.
The catalytic inactivation of Escherichia coli (E. coli) in water by silver loaded alumina as catalyst was investigated. Ag/Al2O3 and AgCl/Al2O3 catalysts exhibited high bactericidal activity at room temperature in water with no need for any light or electrical power input. Dissolved oxygen which can be catalyzed to reactive oxygen species (ROS) was found to be essential for the strong bactericidal activities of the catalysts. Decomposition of the cell wall leading to leakage of the intracellular component and the complete lysis of the whole cell were directly observed by transmission electron microscopy (TEM). The resultant change in cell permeability was confirmed by potassium ion leakage. The different morphological changes between E. coli cells treated with the catalysts and Ag+ were also observed. The formation of ROS involved in the bactericidal process by AgCl/Al2O3 was confirmed by addition of catalase and OH scavenger. Higher temperature and pH value were found to have positive effect on the bactericidal activity of AgCl/Al2O3. All these results indicated that the bactericidal effect of the catalyst was a synergic action of ROS and Ag+, not an additive one. A possible mechanism is proposed. 相似文献
4.
Marie-Anne Tartanson Laurence Soussan Matthieu Rivallin Sophie Pecastaings Cristian V. Chis Diego Penaranda Christine Roques Catherine Faur 《Applied and environmental microbiology》2015,81(20):7135-7142
The bactericidal activity of an Al2O3-TiO2-Ag granular material against an Escherichia coli strain was confirmed by a culture-based method. In particular, 100% of microorganisms were permanently inactivated in 30 to 45 min. The present work aimed to investigate the mechanisms of the bactericidal action of this material and their dynamics on Escherichia coli using different techniques. Observations by transmission electron microscopy (TEM) at different times of disinfection revealed morphological changes in the bacteria as soon as they were put in contact with the material. Notably highlighted were cell membrane damage; cytoplasm detachment; formation of vacuoles, possibly due to DNA condensation, in association with regions exhibiting different levels of electron density; and membrane lysis. PCR and flow cytometry analyses were used to confirm and quantify the observations of cell integrity. The direct exposure of cells to silver, combined with the oxidative stress induced by the reactive oxygen species (ROS) generated, was identified to be responsible for these morphological alterations. From the first 5 min of treatment with the Al2O3-TiO2-Ag material, 98% of E. coli isolates were lysed. From 30 min, cell viability decreased to reach total inactivation, although approximately 1% of permeable E. coli cells and 1% of intact cells (105 genomic units · ml−1) were evidenced. This study demonstrates that the bactericidal effect of the material results from a synergic action of desorbed and supported silver. Supported silver was shown to generate the ROS evidenced. 相似文献
5.
Cheng X Imai T Teeka J Yamaguchi J Hirose M Higuchi T Sekine M 《Applied microbiology and biotechnology》2011,90(4):1493-1500
Little information is available regarding the effectiveness of water disinfection by CO2 at low pressure. The aim of this study was to evaluate the use of high levels of dissolved CO2 at 0.3–0.6 MPa for the inactivation of microorganisms. Bacteriophage T4 was chosen as the model virus and Escherichia coli was selected as the representative bacterium. The results of the study showed a highly effective log inactivation of E. coli and bacteriophage T4 at low and medium initial concentrations by high levels of dissolved CO2 at 0.3 MPa with a treatment time of 20 min. When the pressure was increased to 0.6 MPa, inactivation of both microorganisms
at high initial concentrations was improved to different extents. Neither pressurized air nor O2 effectively inactivated both E. coli and bacteriophage T4. The pH was not a key factor affecting the inactivation process by this method. The results of scanning
electron microscopy of E. coli and transmission electron microscopy of bacteriophage T4 suggested that “CO2 uptake at high pressure and bursting of cells by depressurization” were the main reasons for lethal effect on microorganisms.
This technology has potential for application in the disinfection of water, wastewater, and liquid food in the future. 相似文献
6.
7.
In the presence of hydrogen peroxide, the heme protein lactoperoxidase is able to oxidize thiocyanate and iodide to hypothiocyanite, reactive iodine species, and the inter(pseudo)halogen cyanogen iodide. The killing efficiency of these oxidants and of the lactoperoxidase-H2O2-SCN?/I? system was investigated on the bioluminescent Escherichia coli K12 strain that allows time-resolved determination of cell viability. Among the tested oxidants, cyanogen iodide was most efficient in killing E. coli, followed by reactive iodine species and hypothiocyanite. Thereby, the killing activity of the LPO-H2O2-SCN?/I? system was greatly enhanced in comparison to the sole application of iodide when I? was applied in two- to twenty-fold excess over SCN?. Further evidence for the contribution of cyanogen iodide in killing of E. coli was obtained by applying methionine. This amino acid disturbed the killing of E. coli mediated by reactive iodine species (partial inhibition) and cyanogen iodide (total inhibition), but not by hypothiocyanite. Changes in luminescence of E. coli cells correlate with measurements of colony forming units after incubation of cells with the LPO-H2O2-SCN?/I? system or with cyanogen iodide. Taken together, these results are important for the future optimization of the use of lactoperoxidase in biotechnological applications. 相似文献
8.
Elnaz Mehdizadeh Aghdam Lena Mahmoudi Azar Abolfazl Barzegari Farrokh Karimi Majid Mesbahfar Naser Samadi Mohammad Saeid Hejazi 《Gene》2012
Oxidative stress occurs as a result of imbalance between generation and detoxification of reactive oxygen species (ROS). This kind of stress was rarely discussed in connection with foreign protein production in Escherichia coli. Relation between cytoplasmic recombinant protein expression with H2O2 concentration and catalase activity variation was already reported. The periplasmic space of E. coli has different oxidative environment in relative to cytoplasm and there are some benefits in periplasmic expression of recombinant proteins. In this study, hydrogen peroxide concentration and catalase activity following periplasmic expression of mouse IL-4 were measured in E. coli. After construction of pET2mIL4 plasmid, the expression of recombinant mouse interleukin-4 (mIL-4) was confirmed. Then, the H2O2 concentration and catalase activity variation in the cells were studied in exponential and stationary phases at various ODs and were compared to those of wild type cells and empty vector transformed cells. It was revealed that empty vector introduction and periplasmic recombinant protein expression increased significantly the H2O2 concentration of the cells. However, the H2O2 concentration in mIL-4 expressing cells was significantly higher than its concentration in empty vector transformed cells, demonstrating more effects of recombinant mIL-4 expression on H2O2 elevation. Likewise, although catalase activity was reduced in foreign DNA introduced cells, it was more lowered following expression of recombinant proteins. Correlation between H2O2 concentration elevation and catalase activity reduction with cell growth depletion is also demonstrated. It was also found that recombinant protein expression results in cell size increase. 相似文献
9.
Thymine dimers were irradiated in aqueous solution with 60Co γ-rays in N2 or O2. Thymine and unidentified non-UV-absorbing products appeared. The thymine was identified by spectrophotometry, chromatography, and ability to support the growth of Escherichia coli 15 T-. Residual dimer was determined by a UV-reversibility assay. The G-values for dimer breakage were approximately equal in N2 and O2. At low γ-doses, about two thymines were produced per dimer broken in N2, whereas only about one thymine appeared per dimer broken in O2. For dimer irradiated in frozen solution, the yield of thymine was at least 100 times less than in liquid. 相似文献
10.
Effects of N2-O2 and CO2-O2 Tensions on Growth of Fungi Isolated from Damaged Flue-Cured Tobacco
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ten fungi, Aspergillus niger, A. flavus, A. ochraceus, A. ruber, A. repens, A. amstelodami, Alternaria tenuis, Penicillium brevi-compactum, Cladosporium herbarum, and Chaetomium dolicotrichum, were isolated from moldy flue-cured tobacco and grown in various mixtures of N2-O2 or CO2-O2. A 1 to 5% concentration of O2 in an N2 atmosphere caused the greatest change in growth of the nine species, and a 10 to 20% concentration of O2 for A. flavus. All species, except A. amstelodami and A. ruber, grew faster in air than in mixtures containing 10% O2. High O2 concentrations generally inhibited furrow production in the mycelial mats. In an atmosphere of 5 to 40% O2 in the N2 atmosphere, furrows formed in mycelial mats between 5 and 40% O2 in the species except for A. ruber, A. repens, and A. amstelodami, which produced none in any concentration. As O2 decreased below 20%, spore production was progressively decreased, colony color faded to white, and cleistothecia formation was suppressed. In CO2-O2 mixtures radial growth of all species increased with each quantitative decrease of CO2. All species except A. niger grew faster in air than in 10% CO2. In contrast to N2-O2 mixtures, the fungi formed furrows, sporulation and cleistothecial formation were suppressed, and colony color changed to white in higher O2 concentrations. 相似文献
11.
Endogenous Superoxide Dismutase Levels Regulate Iron-Dependent Hydroxyl Radical Formation in Escherichia coli Exposed to Hydrogen Peroxide
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Michael L. McCormick Garry R. Buettner Bradley E. Britigan 《Journal of bacteriology》1998,180(3):622-625
Aerobic organisms contain antioxidant enzymes, such as superoxide dismutase (SOD) and catalase, to protect them from both direct and indirect effects of reactive oxygen species, such as O2·− and H2O2. Previous work by others has shown that Escherichia coli mutants lacking SOD not only are more susceptible to DNA damage and killing by H2O2 but also contain larger pools of intracellular free iron. The present study investigated if SOD-deficient E. coli cells are exposed to increased levels of hydroxyl radical (·OH) as a consequence of the reaction of H2O2 with this increased iron pool. When the parental E. coli strain AB1157 was exposed to H2O2 in the presence of an α-(4-pyridyl-1-oxide)-N-tert-butyl-nitrone (4-POBN)–ethanol spin-trapping system, the 4-POBN–·CH(CH3)OH spin adduct was detectable by electron paramagnetic resonance (EPR) spectroscopy, indicating ·OH production. When the isogenic E. coli mutant JI132, lacking both Fe- and Mn-containing SODs, was exposed to H2O2 in a similar manner, the magnitude of ·OH spin trapped was significantly greater than with the control strain. Preincubation of the bacteria with the iron chelator deferoxamine markedly inhibited the magnitude of ·OH spin trapped. Exogenous SOD failed to inhibit ·OH formation, indicating the need for intracellular SOD. Redox-active iron, defined as EPR-detectable ascorbyl radical, was greater in the SOD-deficient strain than in the control strain. These studies (i) extend recent data from others demonstrating increased levels of iron in E. coli SOD mutants and (ii) support the hypothesis that a resulting increase in ·OH formation generated by Fenton chemistry is responsible for the observed enhancement of DNA damage and the increased susceptibility to H2O2-mediated killing seen in these mutants lacking SOD. 相似文献
12.
Hidetaka Doi Yasushi Hoshino Kentaro Nakase Yoshihiro Usuda 《Applied microbiology and biotechnology》2014,98(2):629-639
Fatty acids are a promising raw material for substance production because of their highly reduced and anhydrous nature, which can provide higher fermentation yields than sugars. However, they are insoluble in water and are poorly utilized by microbes in industrial fermentation production. We used fatty acids as raw materials for l-lysine fermentation by emulsification and improved the limited fatty acid-utilization ability of Escherichia coli. We obtained a fatty acid-utilizing mutant strain by laboratory evolution and demonstrated that it expressed lower levels of an oxidative-stress marker than wild type. The intracellular hydrogen peroxide (H2O2) concentration of a fatty acid-utilizing wild-type E. coli strain was higher than that of a glucose-utilizing wild-type E. coli strain. The novel mutation rpsA D210Y identified in our fatty acid-utilizing mutant strain enabled us to promote cell growth, fatty-acid utilization, and l-lysine production from fatty acid. Introduction of this rpsA D210Y mutation into a wild-type strain resulted in lower H2O2 concentrations. The overexpression of superoxide dismutase (sodA) increased intracellular H2O2 concentrations and inhibited E. coli fatty-acid utilization, whereas overexpression of an oxidative-stress regulator (oxyS) decreased intracellular H2O2 concentrations and promoted E. coli fatty acid utilization and l-lysine production. Addition of the reactive oxygen species (ROS) scavenger thiourea promoted l-lysine production from fatty acids and decreased intracellular H2O2 concentrations. Among the ROS generated by fatty-acid β-oxidation, H2O2 critically affected E. coli growth and l-lysine production. This indicates that the regression of ROS stress promotes fatty acid utilization, which is beneficial for fatty acids used as raw materials in industrial production. 相似文献
13.
Chapman et al. (B. Chapman, N. Jensen, T Ross, and M. B. Cole, Appl. Environ. Microbiol. 72:5165-5172, 2006) demonstrated that an increased NaCl concentration prolongs survival of Escherichia coli O157 SERL 2 in a broth model simulating the aqueous phase of a food dressing or sauce containing acetic acid. We examined the responses of five other E. coli strains and four Salmonella enterica strains to increasing concentrations of NaCl under conditions of lethal acidity and observed that the average “lag” time prior to inactivation decreases in the presence of hydrochloric acid but not in the presence of acetic acid. For E. coli in the presence of acetic acid, the lag time increased with increasing NaCl concentrations up to 2 to 4% at pH 4.0, up to 4 to 6% at pH 3.8, and up to 4 to 7% (wt/wt of water) NaCl at pH 3.6. Salmonella was inactivated more rapidly by combined acetic acid and NaCl stresses than E. coli, but increasing NaCl concentrations still decreased the lag time prior to inactivation in the presence of acetic acid; at pH 4.0 up to 1 to 4% NaCl was protective, and at pH 3.8 up to 1 to 2% NaCl delayed the onset of inactivation. Sublethal injury kinetics suggest that this complex response is a balance between the lethal effects of acetic acid, against which NaCl is apparently protective, and the lethal effects of the NaCl itself. Compared against 3% NaCl, 10% (wt/wt of water) sucrose with 0.5% NaCl (which has similar osmotic potential) was found to be equally protective against adverse acetic acid conditions. We propose that hypertonicity may directly affect the rate of diffusion of acetic acid into cells and hence cell survival.We previously observed that inactivation of Escherichia coli O157 SERL 2 by acetic acid at adverse pH in a broth model simulating the aqueous phase of acidic sauces and dressings was reduced by the presence of NaCl (4). Specifically, the time to a 3-log10-unit reduction (t3D) of E. coli SERL 2 as function of NaCl concentration was significantly nonmonotonic; that is, the t3D initially increased when NaCl was increased (from 1 to 3% [wt/wt] of solution), but the t3D decreased upon a further increase in NaCl concentration (to 8% [wt/wt] of solution) (4). The statistical significance of this “nonmonotonic” response increased with increasing exposure time from 24 to 72 h (at 23°C), primarily due to a proportionally greater increase in inactivation at 1% (wt/wt) NaCl with increasing treatment time than that which was observed at higher NaCl concentrations (4).The combination of acid and NaCl is a common example of the food industry''s “hurdle” approach, which is used to preserve a large and diverse range of foods, including acidic dressings and sauces, fermented meats, cheeses, and preserved vegetables. Given the widespread use of this hurdle combination in food manufacturing, the first aim of this study was to determine whether the observed protection of E. coli SERL 2 from acid inactivation by NaCl is common among E. coli and Salmonella enterica and at what NaCl concentration maximum protection is achieved. A second aim was to determine whether NaCl protection is specific against acid pH in general or against acetic acid in particular. Third, possible protection against acid inactivation by another osmolyte, sucrose, was assessed to resolve whether the effect is solute specific.When cells are placed in hypertonic environments, plasmolysis occurs as the cytoplasmic volume reduces due to water loss by osmosis. The thin peptidoglycan layer of gram-negative microorganisms is anchored to the cytoplasmic membrane and can be distended by plasmolysis or even ruptured when plasmolysis is more extreme. Decad and Nikaido (5) observed that the cytoplasmic volume in gram-negative microorganisms was reduced to ∼50% at ∼0.3 M NaCl but that the plasmolysis-induced cell wall damage was minimal. At 0.5 M (2.9%, wt/wt) NaCl, however, they observed cell wall damage in a large fraction of cells. Thus, in the experiments described here we explored the mechanism of the protective effect of NaCl, and specifically cell wall damage in E. coli populations simultaneously exposed to NaCl and either acetic or hydrochloric acid (HCl), by enumeration of both injured and noninjured survivors by culture on media with and without bile salts. 相似文献
14.
15.
D. N. Karimova I. V. Manukhov E. Yu. Gnuchikh I. F. Karimov D. G. Deryabin 《Applied Biochemistry and Microbiology》2016,52(3):269-276
The effect of reactive oxygen and nitrogen species on lux-biosensors based on the Escherichia coli K12 MG1655 and Salmonella typhimurium LT2 host strains was investigated. The bioactivity of exogenous free radicals to the constitutively luminescent E. coli strain with plasmid pXen7 decreased in the order H2O2 > OCl– > NO? > RОO? > ONOO–> O2?- while the bioluminescence of S. typhimurium strain transformed with this plasmid decreased in the order NO? > H2O2 > ONOO– > RОO? > OCl– > O2?- The cross-reactivity of induced lux-biosensors to reactive oxygen and nitrogen species, the threshold sensitivity and the luminescence amplitude dependences from the plasmid specificity and the host strain were indicated. The biosensors with plasmid pSoxS′::lux possessed a wider range of sensitivity, including H2O2 and OCl–, along with O2?- and NO?. Among the used reactive oxygen and nitrogen species, H2O2 showed the highest induction activity concerning to the plasmids pKatG′::lux, pSoxS′::lux and pRecA′::lux. The inducible lux-biosensors based on S. typhimurium host strain possessed a higher sensitivity to the reactive oxygen and nitrogen species in comparison with the E. coli lux-biosensors. 相似文献
16.
Effects of Acid Adaptation, Product pH, and Heating on Survival of Escherichia coli O157:H7 in Pepperoni
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Denise C. R. Riordan Geraldine Duffy James J. Sheridan Richard C. Whiting Ian S. Blair David A. McDowell 《Applied microbiology》2000,66(4):1726-1729
The thermotolerance of E. coli O157:H7 cells (strain 380-94) heated in pepperoni is reported. Information on the pattern of thermal inactivation of E. coli O157:H7 in pepperoni was applied in the development of heating processes designed to reduce E. coli O157:H7 numbers therein by 5 log10 units. 相似文献
17.
Saelee N Tonganunt-Srithaworn M Wanna W Phongdara A 《International journal of biological macromolecules》2011,49(1):32-36
Cellular oxidative stress responses are caused in many ways, but especially by disease and environmental stress. After the initial burst of reactive oxygen species (ROS), the effective elimination of ROS is crucial for the survival of organisms and is mediated by antioxidant defense mechanisms. In this paper, we investigate the possible antioxidant function of Penaeus monodon Receptor for Activated C Kinase-1 (Pm-RACK1). When Pm-RACK1 was over-expressed in Escherichia coli cells or Spodoptera frugiperda (Sf9) insect cells exposed to H2O2, it significantly protected the cells from oxidative damage induced by H2O2. When recombinant Pm-RACK1 protein was expressed as a histidine fusion protein in E. coli and purified with a Ni2+-column it possessed antioxidant functions that protected DNA from metal-catalyzed oxidation. Shrimp (Penaeus vannamei) held at an alkaline pH had a much higher hepatopancreatic expression of Pm-RACK1 than in those held at pH 7.4. The exposure of shrimp to alkaline pH is also known to increase ROS production. These results provide strong evidence that Pm-RACK1 can participate in the shrimp antioxidant response induced by the formation of ROS. 相似文献
18.
I. S. Sazykin V. N. Prokofiev V. A. Chistyakov M. A. Sazykina V. V. Vnukov 《Applied Biochemistry and Microbiology》2011,47(4):400-404
A comparative H2O2-luminol- and Fe(II)-induced chemiluminescence analysis of extracts of two strains of marine oil oxidizing bacteria Actinetobacter calcoaceticus cultivated either in the presence or absence of oil was carried out. Effects of these extracts on E. coli MG1655 biosensor (pSoxS-lux) were studed. Activation of H2O2-induced chemiluminescence in the presence of oil was observed. This suggests activation of free radical lipid peroxidation.
Aqueous extracts of microorganisms cultivated in the presence of oil were shown to activate reactive oxygen species production
(ROS) in Fe(II)-induced chemiluminescence reaction mixture. Acetone-ethanol extracts induced antioxidative systems of both
strains. Chemiluminescence analysis in a biological system carried utilizing E. coli MG1655 (pSoxS-lux) revealed that aqueous extracts of the strains cultivated in the absence of oil contained potential antioxidants. 相似文献
19.
Jaroslav Julák Vladimír Scholtz Soňa Kotúčová Olga Janoušková 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2012,28(3):230-239
This article describes and particularly explains a new phenomenon of persistent microbicidal effect of water previously exposed to the low-temperature plasma, which cannot be attributed to the acidification only. The direct microbicidal action of plasma is well documented, being mediated by number of reactive particles with a short lifetime. However, we observed the microbicidal effect also in exposed water stored for a month, where it must be mediated by stable particles. In water and in phosphate-buffered saline, the formation of NOx and corresponding acids, H2O2 and O3 was confirmed after exposition to the low-temperature plasma generated in air by DC negative glow corona and positive streamer discharge. The time course of acidification, H2O2 and O3 formation were deremined. Except uncertain traces of HCN, SIFT-MS analysis of exposed liquids reveals no additional reactive compounds. The microbicidal effect persists almost unchanged during 4 weeks of storage, although O3 completely and H2O2 almost disappears. Staphylococcus epidermidis and Escherichia coli were inactivated within 10 min of incubation in exposed liquids, Candida albicans needs at least 1 h. The solutions prepared by artificial mixing of reactive compounds mimic the action of exposed water, but in lesser extent. The acid milieu is the main cause of the microbicidal effect, but the possibility of still unidentified additional compound remains open. 相似文献
20.
Aqueous leachates prepared from natural antibacterial clays, arbitrarily designated CB-L, release metal ions into suspension, have a low pH (3.4–5), generate reactive oxygen species (ROS) and H2O2, and have a high oxidation-reduction potential. To isolate the role of pH in the antibacterial activity of CB clay mixtures, we exposed three different strains of Escherichia coli O157:H7 to 10% clay suspensions. The clay suspension completely killed acid-sensitive and acid-tolerant E. coli O157:H7 strains, whereas incubation in a low-pH buffer resulted in a minimal decrease in viability, demonstrating that low pH alone does not mediate antibacterial activity. The prevailing hypothesis is that metal ions participate in redox cycling and produce ROS, leading to oxidative damage to macromolecules and resulting in cellular death. However, E. coli cells showed no increase in DNA or protein oxidative lesions and a slight increase in lipid peroxidation following exposure to the antibacterial leachate. Further, supplementation with numerous ROS scavengers eliminated lipid peroxidation, but did not rescue the cells from CB-L-mediated killing. In contrast, supplementing CB-L with EDTA, a broad-spectrum metal chelator, reduced killing. Finally, CB-L was equally lethal to cells in an anoxic environment as compared to the aerobic environment. Thus, ROS were not required for lethal activity and did not contribute to toxicity of CB-L. We conclude that clay-mediated killing was not due to oxidative damage, but rather, was due to toxicity associated directly with released metal ions. 相似文献