介质阻挡气液两相放电灭活大肠杆菌

采用双向窄脉冲介质阻挡气液两相放电技术,对大肠杆菌灭活效果进行了试验.研究了曝气量、初始含菌量、处理时间、电场强度及电导率与大肠杆菌灭活率的关系.结果表明,菌体灭活率随初始含菌量、电场强度、处理时间的增加而增大,但随电导率的增加而减小.较佳的曝气量为0.75m³/h.     

Genotypic characterization of quinolone resistant-Escherichia coli isolates from retail food in Morocco

This study was conducted to assess the retail food as a possible vehicle for antimicrobial resistant, particularly quinolones resistant and pathogenic Escherichia coli. We determined the prevalence and characteristics of nalidixic acid (Nal) resistant E. coli isolates from diverse retail food samples. In all, 70 (28%) of 250 E. coli isolates studied were Nal-resistant E. coli and 91% of these were multi-drug resistant. Plasmid mediated quinolone resistance genes were identified in 32 isolates, including aac(6′)-Ib-cr (n = 16), qnrS1 (n = 11) and qnrB19 (n = 7). Mutations in gyr A and par C genes were detected among 80% of the isolates, and the isolates showed substitution Ser83-Leu and Asp87-Asn in gyrA and Ser80-Ile in parC. In addition, three different gene cassettes were identified (aadA1, aadA7, aac(3)-Id) in 18%. Virulence-associated genes stx1, eae, sfa, hlyA and stx2 were found in six (8%), three (4%), two (3%), three (4%) and three (4%) isolates, respectively. E. coli isolates of phylogenetic group A were dominant (64%, 45/70). Pulsed field gel electrophoresis revealed none epidemiological relationship between these isolates. The results of this work report the higher frequency of Nal-resistant E. coli isolates from Moroccan retail food samples including MDR and pathogenic isolates.     

Population Dynamics of Escherichia coli in Surface Water1

Bucci, Vanni, Marin Vuli?, Xiaodan Ruan, and Ferdi L. Hellweger, 2011. Population Dynamics of Escherichia coli in Surface Water. Journal of the American Water Resources Association (JAWRA) 47(3):611‐619. DOI: 10.1111/j.1752‐1688.2011.00528.x Abstract: Present models of the fate of enteric bacteria in surface water usually assume simple first‐order decay. However, observed decay kinetics are typically biphasic and there is increasing evidence for growth in the ambient environment. These features are similar to the stationary phase of long‐term batch cultures, where the dynamics are the result of repeated cycles of population takeovers by Growth Advantage in Stationary Phase (GASP) mutants able to scavenge nutrients released from dead cells. We investigated the possible role of this mechanism (i.e., growth of an adapted subpopulation) in surface water using laboratory experiments with various strains of Escherichia coli in different types of water. Addition of ampicillin (which only kills dividing cells) to these cultures caused a decrease in the total cell density, demonstrating the presence of a growing subpopulation. Furthermore, long‐term survivors from surface water cultures outcompete naïve cells and take over the population in surface water. This growth advantage is heritable (i.e., aged strains were isolated from a single cell) and consistent with the GASP mechanism, although the responsible loci were not identified. Our results show that E. coli populations in surface water are dynamic and consist of dying naïve cells and growing surface water adapted cells. These results can explain the apparent biphasic decay pattern observed in laboratory experiments. This mechanism may also be important in the ambient environment.     

群体感应信号分子存在下磺胺对大肠杆菌生长、突变及R388质粒接合转移的影响

抗生素的滥用使细菌耐药性问题日益突出,给许多疾病的预防与控制增加了难度。基因突变和质粒接合转移是细菌获得抗生素抗性基因的主要方式,许多研究围绕抗性基因来展开,但是关于群体感应对于抗性基因产生和传播的影响鲜有报道。本文以大肠杆菌(Escherichia coli)为模式生物,群体感应信号分子N-(β-酮己酰)-L-高丝氨酸内酯(3-oxo-C6-HSL,C6)和3种磺胺类抗生素(磺胺嘧啶、磺胺甲恶唑、磺胺氯哒嗪)为研究对象,测定了其对大肠杆菌生长效应、突变效应及接合转移效应的影响。结果表明:C6不影响磺胺对大肠杆菌的生长抑制率,但能够削弱磺胺对大肠杆菌突变的促进作用,并且能增强磺胺对大肠杆菌R388质粒接合转移的抑制作用。本文为从群体感应角度研究大肠杆菌耐药性的产生与传播提供新思路。     

ACCOMMODATING CHANGE OF BACTERIAL INDICATORS IN LONG TERM WATER QUALITY DATASETS1

ABSTRACT: In 1996, the State of Oregon adopted a water quality standard based on Escherichia coli (E. coli), recognizing E. coli as an indicator of pathogenic potential. The Oregon Department of Environmental Quality (DEQ) began analysis for E. coli that same year. The Oregon DEQ continued collection and analysis of fecal coliform (a prior indicator organism) for data input to bacterial loading models and the Oregon Water Quality Index (OWQI). The OWQI is a primary indicator of general water quality for the Oregon DEQ and the Oregon Progress Board. The objective of this study was to develop a regression relationship between fecal coliform and E. coli. This relationship would fill data gaps and extend water quality models and indicators. Water quality policy is better informed by the ability of these extended water quality models to determine whether water quality meets present or would have met past bacterial standards. Monitoring resources spent on dual bacterial analyses could be conserved. This study also showed that changes to OWQI values (as a result of changing bacterial indicators) were minimal, and corresponded to improved characterization of water quality with respect to pathogenic potential.     

ESCHERICHIA COLI SURVIVAL IN MANTLED KARST SPRINGS AND STREAMS,NORTHWEST ARKANSAS OZARKS,USA1

Recent studies indicate fecal coliform bacterial concentrations, including Escherichia coli (E. coli), characteristically vary by several orders of magnitude, depending on the hydrology of storm recharge and discharge. E. coli concentrations in spring water increase rapidly during the rising limb of a storm hydrograph, peak prior to or coincident with the peak of the storm pulse, and decline rapidly, well before the recession of the storm hydrograph. This suggests E. coli are associated with resuspension of sediment during the onset of turbulent flow, and indicates viable bacteria reside within the spring and stream sediments. E. coli inoculated chambers were placed in spring and stream environments within the mantled karst of northwest Arkansas to assess long term (> 75 days) E. coli viability. During the 75‐day study, a 4‐log die‐off of E. coli was observed for chambers placed in the Illinois River, and a 5‐log die‐off for chambers placed in Copperhead Spring. Extrapolation of the regression line for each environment indicates E. coli concentration would reach 1 most probable number (MPN)/100 g sediment at Copperhead Spring in about 105 days, and about 135 days in the Illinois River, based on a starting inoculation of 2.5 × 107 MPN E. coli/100 g of sediment. These in situ observations indicate it is possible for E. coli to survive in these environments for at least four months with no fresh external inputs.     

二氧化钛光催化氧化杀菌的研究及进展

本文概括了光催化氧化杀菌的发展历史 ,以及最新的研究进展 ,综合分析了其杀菌机理和影响反应的各相关因素 ,并为今后的发展提出了一些看法     

芜菁花叶病毒杭州株P1基因的克隆和在大肠杆菌中的表达

通过反转录ＰＣＲ，克隆得到１．２ｋｂ的ＴｕＭＶＨ１的Ｐ１片段，并在大肠杆菌表达载体ｐＧＥＭＥＸ－１中得以表达，表达产物为可融性融合蛋白，Ｍｒ≈６×１０４．     

地衣芽孢杆菌2709和 6816碱性蛋白酶基因在大肠杆菌中的克隆、表达及序列分析

用PCR方法从地衣芽孢杆菌 2 70 9和 6 816中扩增了碱性蛋白酶基因 (apr1和apr2 ) ,扩增的DNA片段插入到大肠杆菌载体 pET -2 8a中 ,构建成重组分泌型表达载体pAPR1、pAPR2 .pAPR1、pAPR2中碱性蛋白酶基因在大肠杆菌宿主JM 10 9(DE3)中得到表达 .SDS -PAGE分析显示融合表达产物的分子量均为 30 .5× 10 3 ,同核酸序列测定所推导的值相符 .表达产物分别占细胞总蛋白的 8.0 %和 7.5 % .2 70 9重组菌所得酶活为 12 10u/mL ,6 816重组菌所得酶活为 1175u/mL .研究发现 ,重组的碱性蛋白酶在进入大肠杆菌周质空间时可能存在前肽自动脱落的现象 .同时 ,对地衣芽孢杆菌 2 70 9碱性蛋白酶基因序列进行了测定和比较分析 ,发现与地衣芽孢杆菌 6 816碱性蛋白酶基因的同源性为 98% .图 5参 11     

紫外线杀菌效能的研究

自来水的消毒目前普遍采用氯及含氯化合物药剂，消毒过程中产生三卤甲烷等致癌或致突变物质，从而造成水体的二次污染，许多国家已经禁止在消毒中使用含氯药剂。因此，具有安全可靠高效杀菌作用的紫外线消毒技术逐渐发展起来，并越来越受到人们的关注。但是紫外线的使用也有一定的限制，通过紫外线照射时间及进水浊度的变化，研究了具有一定照射强度的紫外灯的杀菌效能变化，并得出了紫外线具有最佳杀菌效果的进水极限浊度和照射时间。同时还研究了紫外线对具有不同抗性的细菌的系灭效率，为饮用水和污水的消毒处理提供了实验基础。