静磁场对大肠杆菌生长过程的作用机制研究

通过对在外加静磁场和正常情况下培养大肠杆茵生长情况的对比分析,发现试验条件下所选磁场对大肠杆茵有明显促进生长的作用,茵落计数结果表明磁场越强作用效果越明显。对试验结果进行Dunnettt检验发现均具有差异显性。     

静磁场对单株人体体表正常菌生长影响的研究

本文通过40mT和120mT两种静磁场作用下表皮葡萄球菌生长过程的研究,发现试验所选强度静磁场加速了表皮葡萄球菌在对数生长期的生长速率,而在进入稳定生长期后其生长速率反而低于对照组,但就整个生长周期而言,静磁场作用下表皮葡萄球菌的总量大于对照组,表明了试验所选静磁场对表皮葡萄球菌生长有一定促进作用。     

磁场对大肠杆菌生长影响的研究

通过对在外加恒强磁场与正常情况下培养的大肠杆菌的生长曲线的测定及对比分析,发现外加磁场能影响大肠杆菌正常的生长并能使其世代周期延长。     

静磁场对单株人体体表正常菌生长影响的研究

本文通过40mT和120mT两种静磁场作用下表皮葡萄球菌生长过程的研究,发现试验所选强度静磁场加速了表皮葡萄球菌在对数生长期的生长速率,而在进入稳定生长期后其生长速率反而低于对照组,但就整个生长周期而言,静磁场作用下表皮葡萄球菌的总量大于对照组,表明了试验所选静磁场对表皮葡萄球菌生长有一定促进作用.     

恒定磁场对大肠杆菌生长繁殖影响

目的:研究恒定磁场在静态处理和动态处理两种处理方式下对大肠杆菌生长繁殖的影响.方法:将处于对数生长期的大肠杆菌茵液置于磁场中(静态处理)或使菌液循环流动并通过磁场(动态处理),用平板法测定不同时刻菌液的活菌数,记录下菌落形成单位(CFU)的数目,并与相应时申刻对照样(无磁处理)的CFU作对比.结果:两种处理方式下,菌液的相对CFU的数目都有下降.且动态处理的下降幅度大于静态处理.结论:恒定磁场在两种处理方式下都对大肠杆菌起到明显的杀死或抑制作用.文章的讨论部分总结了产生这种作用的可能机理.     

AgNO3对大肠杆菌和金黄色葡萄球菌的抗菌作用及机制

以大肠杆菌和金黄色葡萄球菌为模式菌,对AgNO3的抗菌效果进行研究,并对其抗菌机制作初步探讨。AgNO3对大肠杆菌的抑制生长曲线表明:2.891 mg/L的AgNO3能够完全抑制106个/mL的大肠杆菌细胞生长,AgNO3使大肠杆菌和金黄色葡萄球菌的延滞期加长,并且浓度越高,延滞期越长。另外,AgNO3对大肠杆菌和金黄色葡萄球菌脱氢酶的活性有明显影响,随着AgNO3浓度的提高,脱氢酶的活性逐渐降低。AgNO3溶液作用于细菌后,细菌表面疏水性均有不同程度地下降,且浓度越大对其影响也越明显,大肠杆菌的下降程度要大于金黄色葡萄球菌。     

壳聚糖对大肠杆菌的抑制作用规律及抗菌机理初探

考察了不同分子量壳聚糖对大肠杆菌的抑菌性能,利用壳聚糖的席夫碱反应对其氨基加以保护,探讨了壳聚糖对大肠杆菌的抗菌机理。研究结果表明:壳聚糖分子量越小,对大肠杆菌的抗菌作用越明显;壳聚糖对大肠杆菌的抑菌作用与其氨基的质子化有关。     

大肠杆菌抗氧化系统-oxyR调节子对细菌生长繁殖的调控作用

oxyR调节子是最早发现的细菌抗氧化防御系统之一,大肠杆菌oxyR调节子中参与抗氧化作用的基因成员包括katG、ahpC、ahpF等,通过对H2O2及过氧化物等的直接清除方式发挥作用。虽然该方面的研究很多,但对于大肠杆菌oxyR调节子对细菌生长繁殖的影响尚不清楚。通过对大肠杆菌oxyR、ahpCF、katE/G基因突变菌株进行研究,突变体JI370中ahpCF基因缺失导致其内源H2O2积累减少使其生长相应加快,而对于katG和katE基因突变体JI367和ahpCF、oxyR基因突变体LC74来说,胞内H2O2极显著上升会抑制细菌生长,并且H2O2积累量越大对其生长抑制作用越明显。与野生型菌株相比,ahpCF的缺失突变菌株JI370和ahpCF及oxyR双突变的LC74在菌株生长的潜伏期受到更显著的影响。结果表明:在CAT(catalase,CAT)与AHP(alkyl hydroperoxide reductase,AHP)协同清除内源H2O2的作用中,AHP起到主导作用,并且在细菌的生长繁殖中,ahp基因起到重要的作用。     

花生种子的磁处理对其萌发及幼苗生长的影响

本试验着重研究了用交、直流磁场对花生种子进行处理后,在种子萌发及幼苗生长过程中产生的影响。结果表明,一定强度的交流或直流磁场对种子的萌发及幼苗生长有一定的促进作用。处理过的种子存放一年后,磁场对种子萌发的作用依然存在。     

稳恒磁场联合抗肿瘤药物协同杀伤肝癌细胞Hepa1-6

化学疗法为肿瘤临床治疗的常规方法,存在毒副作用大、抗药性强等缺陷。为了提高药物的利用效率,减少药物引起的毒副作用,将8.8 m T稳恒磁场分别与顺铂、阿霉素联用,经MTT检测发现磁场与药物联用可对肝癌细胞Hepa1-6生长具有协同抑制的效应,经HE染色发现联合处理组细胞发生明显的形态学改变。流式细胞仪检测显示磁场能增加顺铂对G2/M期细胞的滞留,而磁场与阿霉素共同作用可将细胞阻止于G1期和G2/M期。经彗星电泳检测表明磁场能够增强药物对DNA的损伤,且原子力显微镜观察发现联合处理组细胞膜表面出现较大且较深的孔洞,表面结构破坏严重。实验结果表明,抗肿瘤药物与磁场联用技术可有效抑制肿瘤细胞的生长,减少药物的使用浓度,为将抗肿瘤药物与磁场应用于临床治疗恶性肿瘤提供了一个全新的思路与策略。     

Effect of static magnetic field on E. coli cells and individual rotations of ion-protein complexes

The effect of week static magnetic fields on Escherichia coli K12 AB1157 cells was studied by the method of anomalous viscosity time dependencies (AVTD). The AVTD changes were found when E. coli cells were exposed to static fields within the range from 0 to 110 microT. The dependence of the effect on the magnetic flux density had several extrema. These results were compared with theoretical predictions of the ion interference mechanism. This mechanism links the dissociation probability of ion--protein complexes to parameters of magnetic fields. The mechanism was extended to the case of rotating complexes. Calculations were made for several ions of biological relevance. The results of simulations for Ca(2+), Mg(2+), and Zn(2+) showed a remarkable consistency with experimental data. An important condition for this consistency was that all complexes rotate with the same speed approximately 18 revolutions per second (rps). This suggests that the rotation of the same carrier for all ion--protein complexes may be involved in the mechanism of response to the magnetic field. We believe that this carrier is DNA.     

Increased antibiotic resistance of E. coli exposed to static magnetic fields

The present study demonstrates that exposure of bacteria to medium strength static magnetic fields can significantly alter antibiotic sensitivity. Cultures of Escherichia coli were exposed to fields produced by permanent magnets. Samples of bacterial cultures continuously growing in the presence and in the absence of static magnetic fields were left untreated or were treated with an antibiotic and measured at 45 min intervals for cell growth and survival. It was found that exposure of E. coli to the static fields significantly increased antibiotic resistance. Bioelectromagnetics 22:129-137, 2001. Published 2001 Wiley-Liss, Inc.     

The effects of the microwaves on E. coli cells depend on oxygen concentration and static magnetic field

The effects of non-thermal microwaves (MW), 10(-4) and 10(-10) W/cm(2), on conformation of nucleoids in E. coli cells were analyzed by the method of anomalous viscosity time dependence (AVTD). MW exposure was performed at different values of static magnetic field and concentration of oxygen, 8-90 microT, and 2.3-7.8 mg/l, respectively. It was shown, that slight changes in both static magnetic field and oxygen concentration result in significant changes of MW effects up to their disappearance. It was established, that changes in static magnetic field affected significantly the time kinetics of the MW effects. The obtained data provide further evidence for strong dependence of the effects of non-thermal microwaves on physical parameters of exposure and physiological factors. These dependences should be taken into account in replication studies. The obtained results encourage further investigation of possible modulation of non-thermal MW effects by additional electromagnetic fields.     

Effects of static magnetic field on magnetosome formation and expression of mamA,mms13, mms6 and magA in Magnetospirillum magneticum AMB‐1

Magnetotactic bacteria produce nanometer‐size intracellular magnetic crystals. The superior crystalline and magnetic properties of magnetosomes have been attracting much interest in medical applications. To investigate effects of intense static magnetic field on magnetosome formation in Magnetospirillum magneticum AMB‐1, cultures inoculated with either magnetic or non‐magnetic pre‐cultures were incubated under 0.2 T static magnetic field or geomagnetic field. The results showed that static magnetic field could impair the cellular growth and raise C_mag values of the cultures, which means that the percentage of magnetosome‐containing bacteria was increased. Static magnetic field exposure also caused an increased number of magnetic particles per cell, which could contribute to the increased cellular magnetism. The iron depletion in medium was slightly increased after static magnetic field exposure. The linearity of magnetosome chain was also affected by static magnetic field. Moreover, the applied intense magnetic field up‐regulated mamA, mms13, magA expression when cultures were inoculated with magnetic cells, and mms13 expression in cultures inoculated with non‐magnetic cells. The results implied that the interaction of the magnetic field created by magnetosomes in AMB‐1 was affected by the imposed magnetic field. The applied static magnetic field could affect the formation of magnetic crystals and the arrangement of the neighboring magnetosome. Bioelectromagnetics 30:313–321, 2009. © 2009 Wiley‐Liss, Inc.     

Magnetic field exposure induces DNA degradation

In our earlier experiments, we discovered that magnetic field exposure could bring both stabilizing and destabilizing effects to the DNA of Escherichia coli, depending on our parameters of assessment, and both of these effects were associated with the induced synthesis of the heat shock proteins Hsp70/Hsp40 (DnaK/DnaJ). These contradicting results prompted us to explore in this study the effect of magnetic field exposure on the DNA stability in vivo when the heat shock response of the cell was suppressed. By using plasmid pUC18 in E. coli as the indicator, we found that without the protection of the heat shock response, magnetic field exposure indeed induced DNA degradation and this deleterious effect could be diminished by the presence of an antioxidant, Trolox C. In our in vitro test, we also showed that the magnetic field could potentiate the activity of oxidant radicals.     

0.2 T magnetic field inhibits angiogenesis in chick embryo chorioallantoic membrane

Inhibition of angiogenesis is a major target in the fight against cancer and other diseases. Although the effects of static magnetic fields on cancer development and cell growth have been investigated, effects on angiogenesis have received no attention so far. In this study we report the effects on angiogenesis of exposure to 0.2 T static magnetic field. Angiogenesis was analyzed using the chick embryo chorioallantoic membrane assay. Exposure to 0.2 T static magnetic field was achieved by placing the eggs for 3 hr in the isocentre of the magnet of a sectorial magnetic resonance tomograph used in clinical practice. In sham exposed specimens treated with phosphate buffered saline (negative control), no significant vascular reaction was detectable; 3 hr exposure to 0.2 T static magnetic field did not affect the basal pattern of vascularization or chick embryo viability. Prostaglandin E1 and fetal calf serum elicited a strong angiogenic response in sham exposed eggs. This angiogenic response was significantly inhibited by 3 hr exposure to 0.2 T static magnetic field. These findings point to possible use of static magnetic field in inhibiting angiogenesis; this effect could be exploited for treatment of cancer and other diseases where excessive angiogenesis is involved.     

Sources of Escherichia coli in a coastal subtropical environment

Sources of Escherichia coli in a coastal waterway located in Ft. Lauderdale, Fla., were evaluated. The study consisted of an extensive program of field measurements designed to capture spatial and temporal variations in E. coli concentrations as well as experiments conducted under laboratory-controlled conditions. E. coli from environmental samples was enumerated by using a defined substrate technology (Colilert-18). Field sampling tasks included sampling the length of the North Fork to identify the river reach contributing high E. coli levels, autosampler experiments at two locations, and spatially intense sampling efforts at hot spots. Laboratory experiments were designed to simulate tidal conditions within the riverbank soils. The results showed that E. coli entered the river in a large pulse during storm conditions. After the storm, E. coli levels returned to baseline levels and varied in a cyclical pattern which correlated with tidal cycles. The highest concentrations were observed during high tide, whereas the lowest were observed at low tide. This peculiar pattern of E. coli concentrations between storm events was caused by the growth of E. coli within riverbank soils which were subsequently washed in during high tide. Laboratory analysis of soil collected from the riverbanks showed increases of several orders of magnitude in soil E. coli concentrations. The ability of E. coli to multiply in the soil was found to be a function of soil moisture content, presumably due to the ability of E. coli to outcompete predators in relatively dry soil. The importance of soil moisture in regulating the multiplication of E. coli was found to be critical in tidally influenced areas due to periodic wetting and drying of soils in contact with water bodies. Given the potential for growth in such systems, E. coli concentrations can be artificially elevated above that expected from fecal impacts alone. Such results challenge the use of E. coli as a suitable indicator of water quality in tidally influenced areas located within tropical and subtropical environments.     

Effects of static magnetic fields at the cellular level

There have been few studies on the effects of static magnetic fields at the cellular level, compared to those of extremely low frequency magnetic fields. Past studies have shown that a static magnetic field alone does not have a lethal effect on the basic properties of cell growth and survival under normal culture conditions, regardless of the magnetic density. Most but not all studies have also suggested that a static magnetic field has no effect on changes in cell growth rate. It has also been shown that cell cycle distribution is not influenced by extremely strong static magnetic fields (up to a maximum of 10 T). A further area of interest is whether static magnetic fields cause DNA damage, which can be evaluated by determination of the frequency of micronucleus formation. The presence or absence of such micronuclei can confirm whether a particular treatment damages cellular DNA. This method has been used to confirm that a static magnetic field alone has no such effect. However, the frequency of micronucleus formation increases significantly when certain treatments (e.g., X-irradiation) are given prior to exposure to a 10 T static magnetic field. It has also been reported that treatment with trace amounts of ferrous ions in the cell culture medium and exposure to a static magnetic field increases DNA damage, which is detected using the comet assay. In addition, many studies have found a strong magnetic field that can induce orientation phenomena in cell culture.