Accurate assessment of antibiotic susceptibility and screening resistant strains of a bacterial population by linear gradient plate

The dynamics of a bacterial population exposed to the minimum inhibitory concentration （MIC） of an antibiotic is an important issue in pharmacological research. Therefore, a novel antibiotic susceptibility test is urgently needed that can both precisely determine the MIC and accurately select antibiotic-resistant strains from clinical bacterial populations. For this purpose, we developed a method based on Fick＇s laws of diffusion using agar plates containing a linear gradient of antibiotic. The gradient plate contained two layers. The bottom layer consisted of 15 mL agar containing the appropriate concentration of enrofloxacin and allowed to harden in the form of a wedge with the plate slanted such that the entire bottom was just covered. The upper layer consisted of 15 mL plain nutrient agar added with the plate held in the horizontal position. After allowing vertical diffusion of the drug from the bottom agar layer for 12 h, the enrofloxacin concentration was diluted in proportion to the ratio of the agar layer thicknesses. The uniform linear concentration gradient was verified by measuring the enrofloxacin concentration on the agar surface. When heavy bacterial suspensions were spread on the agar surface and incubated for more than 12 h, only resistant cells were able to form colonies beyond the boundary of confluent growth of susceptible cells. In this way, the true MIC of enrofloxacin was determined. The MICs obtained using this linear gradient plate were consistent with those obtained using conventional antibiotic susceptibility tests. Discrete colonies were then spread onto a gradient plate with higher antibiotic concentrations; the boundary line increased significantly, and gene mutations conferring resistance were identified. This new method enables the rapid identification of resistant strains in the bacterial population. Use of the linear gradient plate can easily identify the precise MIC and reveal the dynamic differentiation of bacteria near the MIC. This method allows the study of genetic and physiological characteristics of individual strains, and may be useful for early warning of antibiotic resistance that may occur after use of certain antirnicrobial agents, and guide clinical treatment.

A new device for stress monitoring in continuously welded rails using bi-directional strain method

The technology of continuously welded rails （CWRs） is important in modern railway track structures. To measure rail stress, resistance strain gauges are preferred due to their good stability, sensitivity, and esistance to external interference. Based on the bi-directional strain method, we present a new method for measuring longitudinal rail stress using resistance strain gauges and develop a monitoring device for rail stress to realize long-term and multi-point measurement. Also relevant experimental verification and analysis are conducted. Results indicate that under various constraints the rail stress–strain values can be calculated just with the measured total longitudinal strain and total vertical strain. Considering the measurement error caused by sectional feature of sensors, we put forward a correction equation applicable to different stress conditions. Although the temperature values of the four full-bridge stress gauges can offset each other, the measurement error caused by rail flexural strain can also be eliminated to a certain extent at the same time, the nonuniform distribution of rail cross section temperature and unbalanced flexural strain still affect the measurement error. The experimental results also show that the developed rail-stress-monitoring sensor is suitable for measuring rail stress with reliable working performance.

THE STRESS-STRAIN-RESISTANCE RELATIONS IN Fe-Mn-Si ALLOYS

The stress-strain-resistance relations of the Fe-Mn-Si alloys with different Si content have been investigated by measuring strain (ε) and resistance (△ R/R) upon tension synchronously. The results show that the strum induced γ→ε martensitic transfor- mation increases the strain sensitivity coeffcient of resistance (K) for the Fe-Mn-Si alloys in plastic region. There is a critical strum where dσ/dε becomes a constant value. Si increases the critical strum. A correlation between the critical strain and shape memory effect (SME) in the Fe-Mn-Si alloys is suggested.

THE EFFECT OF COLD DEFORMATION AND HEAT TREATMENT ON COEFFCIENT OF STRAIN RESISTANCE

The coefficient of strain resistance for metals,solid solutions and ordering alloys in annealing state decreases,while K increases in cold working state.The value K of pure metals and solid solutions invaraibly decreases with temperature increass.The main factors influencing the coefHcient of strain resistance are crystal defect,dispersion and degree of atomic arrangement.

Design and validation of wireless strain test system for bridge based on the resistance strain sensor

In order to achieve an access to strain sensor data with wireless transmission in bridge engineering structure testing, a wireless strain test system is presented based on the resistance strain sensor of networks. The wireless bridge strain test system composed of master station and substation adopts the wireless method to realize the high accuracy data acquisition between the master station and the substation under a reliable communication protocol. The system has been tested in contrast with the present strain apparatus. Results show that the wireless system is high-reliable, and has many characteristics such as high efficiency, good precision, high stability with low cost, and good flexibility, without using the present communication network.

Evaluatien of Near-lsogenic Rice Lines with 8 Genes for Bacterial Blight Resistance to Strains in China

A set of near-isogenic rice lines withmonogenic resistance to bacterial blight weredeveloped by IRRI.The Cultivar IR24 wasused as the recurred parent.They wereevaluated with 6 races of Xanthomonascampestris pv.oryzae(Xco)in the Philip-pines at the maximum tillering and the bootingstages by ZHANG and MEW at IRRI in 1989.

电测法测定压力容器应力集中系数

电测法作为一种实验测定应力方法,普遍用于压力容器各点处的压力测定。许多文献还将其所测得的值与解析解或有限元解作了比较,得到了一致的或在趋势走向上一致的结论。但值得注意的是在压力容器变形不协调部位不仅应力值增加,同时主应力的方向也会改变,认为在应用电测法测定压力容器应力最大值求应力集中系数时,存在一些不精确之处。

电测法测定压力容器应力集中系数

电测法作为一种实验测定应力方法 ,普遍用于压力容器各点处的压力测定。许多文献还将其所测得的值与解析解或有限元解作了比较 ,得到了一致的或在趋势走向上一致的结论。但值得注意的是在压力容器变形不协调部位不仅应力值增加 ,同时主应力的方向也会改变。本文认为在应用电测法测定压力容器应力最大值求应力集中系数时 。

棉叶螨抗性培育及交互抗性研究

用久效磷、氯氟氰菊酯和三氯杀螨醇进行模拟抗性培育结果，以抗三氯杀螨醇叶螨种群的抗性增长速度最快，汰选１７次时，抗性高达１３１３倍；抗氯氟氰菊酯种群次之，抗性为２Ｏ５倍（汰选２Ｏ次）；抗久效磷种群为最慢，抗性为１３倍（汰选２Ｏ次）。田间抗性监测，棉叶螨对三氯杀螨醇的搞性发展速度较慢，抗性水平较低与室内汰选结果不同。这可能与田间棉叶螨为复合种群和环境条件不同有关。用上三个种群对１３种杀虫杀螨剂进行交互抗性研究。抗久效磷种群测定结果，久效磷与氧乐果、水胺硫磷、氟氟氰菊脂和双甲眯之间都有交互抗性，以氯氟氰菊酯的交互抗牲更强（１３１倍），与氟氯菊酯、甲氰菊酯和其他选择性杀螨剂如三氯杀螨时、泱螨酯、克螨特、唑螨酯、三唑锡等均无交互搞性；用抗氯氟氰菊酯种群测定结果，氯氟氰菊酯与甲氰菊酯有交互抗牲，与氟氟菊酯、久效磷、氧乐果、水胺硫磷以及其他选择性杀螨剂等均无交互抗性，但与双甲脉和哎螨灵之间有负交互抗性；用抗三氯杀螨时种群测定结果，三氯杀蜗醇与结构非常相似的溴螨酯以及氯氟氰菊酯有很强的交互抗性，与哎螨灵、三唑锡和双甲眯之间有负交互抗性，以双甲眯最明显，与甲氰菊酯。

基于Arruda-Boyce形式的抗冲瓦黏超弹性本构模型研究

根据橡胶材料不可压缩性假设,利用超弹性理论推导出了单轴应力状态下橡胶Arruda-Boyce超弹性模型应力应变关系。结合橡胶抗冲瓦试件单轴拉压实验数据,利用多元线性回归法拟合得到Arruda-Boyce超弹性本构模型参数μ和λm。同时利用Modelcenter集成Abaqus探讨了黏超弹性参数对抗冲瓦结构抗冲击性能的影响。结果表明:同其它几种橡胶常用超弹性模型相比,Arruda-Boyce超弹性模型拟合得到的曲线精度最好。抗冲瓦手性结构的抗冲击性能随着参数μ的增大和λm的减小而降低。

High Frequency of Antiviral Resistance Mutations in HBV Genotypes A2 and H: Multidrug Resistance Strains in Mexico

Background and Aims:Lamivudine(3TC),telbivudine(LdT),entecavir(ETV),adefovir(ADF),and tenofovir(TFV)are drugs used to treat hepatitis B virus(HBV)infection,but specific mutations allow some viruses to become resistant to antiviral drugs or to acquire immune escape capacities.These mutations have not been thoroughly investigated in Mexico.This study aimed to estimate the prevalence of HBV antiviral resistance and escape mutations.Methods:This cross-sectional study analyzed 158 samples.HBV DNA was extracted,amplified,and sequenced in serum samples using the spin column method,PCR assay,and Sanger’s sequencing,respectively.HBV genotypes were determined,and HBV mutations were tested using the Geno2pheno tool.Results:Overall,68.4%(108/158)of HBV patients were infected with genotype H,followed by G(11.4%,18/158),A2(10.8%,17/158),F1b(6.9.0%,11/158),D(1.9%,3/158),and E(0.6%,1/158),and 5.1%(8/158)had evidence of recombination.The prevalence of resistance mutations was 8.2%(13/158)and the most common combined mutation was rt180M+rt204V.Notably,we found the combinations rt180M+rt204V+rt173L(n=2)and rt180M+rt204V+rt202G(n=1)that confer multidrug resistance to 3TC,LdT,and ETV.Resistance mutations were found in genotypes A2(11.8%,2/17),and H(10.2%,11/108),and escape mutations were detected in HBV genotypes A2(11.8%,2/17),H(10.2%,11/108),F1b(9.1%,1/11)and G(5.6%,1/18).Conclusions:The highest prevalence of antiviral resistance mutations or escape mutations was detected in HBV genotypes A2 and H.The earliest cases of HBV multidrug resistance were detected in Mexico.

Molecular characterization and antibacterial effect of endophytic actinomycetes Nocardiopsis sp. GRG1 (KT235640) from brown algae against MDR strains of uropathogens

Our study is to evaluate the potential bioactive compound of Nocardiopsis sp.GRG1(KT235640)and its antibacterial activity against multi drug resistant strains(MDRS)on urinary tract infections(UTIs).Two brown algae samples were collected and were subjected to isolation of endophytic actinomycetes.100 strains of actinomycetes were isolated from algal samples based on observation of morphology and physiological characters.40 strains were active in antagonistic activity against various clinical pathogens.Among the strains,10 showed better antimicrobial activity against MDRS on UTIs.The secondary metabolite of Nocardiopsis sp.GRG1(KT235640)has showed tremendous antibacterial activity against UTI pathogens compared to other strains.Influence of various growth parameters were used for synthesis of secondary metabolites,such as optimum pH 7,incubation time 5e7 days,temperature(30
C),salinity(5%),fructose and mannitol as the suitable carbon and nitrogen sources.At 100 μg/ml concentration MIC of Nocardiopsis sp.GRG1(KT235640)showed highest percentage of inhibition against Proteus mirabilis(85%),and E.coli,Staphylococcus auerues,Psuedomonas aeroginasa,Enterobactor sp and Coagulinase negative staphylococci 78e85%respectively.

Antibacterial activity of selected marine macro algae against vancomycin resistant Enterococcus faecalis

Objective:To evaluate the antibacterial activity of different extracts of Caulerpa chemnitzia(Epser)J.V.Lamououx,Caulerpa racemosa(Frosk.)Weber-van-Bosse(C.racemosa),Caulerpa scalpelliformis(R.Br.)Weber-van-Bosse,Ulva lactuca Lin,Ulva fasciata Dellie,Ulva reticulata Forsk,Stoechospermum marginatum(Ag.)Kutz(S.marginatum),Sargassum wightii Grev,Gracilaria verrucosa(Huds.)Papenfuss and Gracilaria edulis(S.G.Gemelin)P.C.Silva against Enterococcus faecalis(MTCC 439)(E.faecalis)and one clinical isolate of vancomycin resistant E.faecalis.Methods:The selected marine macro algae were extracted with different solvents viz.,hexane,chloroform,ethyl acetate,acetone and methanol.Antibacterial assay was carried out by using disc diffusion method,determination of minimum inhibitory concentration and minimum bactericidal concentration.Results:The maximum antibacterial activity was recorded in the ethyl acetate extracts of S.marginatum and C.racemosa than the other extracts.The mean zone of inhibition produced by the extracts in agar diffusion assays against the tested bacterial strains ranged from 7.1 to 14.5 mm.The minimum inhibitory concentration was between 250 and 500μg/mL,while the minimum bactericidal concentration was from 500 to 1000μg/mL.The ethyl acetate extracts of the seaweeds showed the presence of strong terpenoids,tannins and phenolic compounds compared with the other solvent extracts.Conclusions:These findings suggest that ethyl acetate extracts of S.marginatum and C.racemosa can be used as an antibacterial substance for the treatment of infection caused by E.faecalis.

生物质衍生碳在电阻式应变/压力传感器中的最新应用进展与关键挑战

近年来电阻式应变/压力传感器在运动行为监测、人类健康诊断和人机交互等领域展现了不可替代的作用,因而刺激了人们对其需求的急剧增长.材料和结构设计对电阻式应变/压力传感器的性能有着不可忽视的影响,而生物质碳(BDCs)具有丰富的来源、多样的结构和令人满意的导电性等优良特性,被认为是制造电阻式应变/压力传感器的优异候选材料之一.本综述介绍了BDCs材料在电阻式应变/压力传感器领域的最新进展及其目前面临的主要挑战.首先,系统地概述和讨论了已报道的电阻式应变/压力传感器的分类方法、评价标准和传感机制.其次,总结了具有不同宏观结构(包括一维、二维和三维结构)的BDCs材料的制备及其在电阻式应变/压力传感器领域的最新应用进展.详细分析了具有不同宏观结构的BDCs材料在电阻应变/压力传感器领域的各自应用优势,并讨论了不同宏观结构与器件综合传感性能之间的关系.最后,提出了基于BDCs材料的电阻式应变/压力传感器的未来前景和主要挑战,及其未来发展的研究方向.