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1
Kacem, Majdi. „Inactivation bactérienne par photocatalyse hétérogène : application à Escherichia Coli“. Thesis, Perpignan, 2015. http://www.theses.fr/2015PERP0018/document.
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L’étude présentée dans ce mémoire s’inscrit dans le cadre de la réutilisation des eaux usées traitées par un procédé d’oxydation avancée (AOP), la photocatalyse hétérogène. Ce procédé, couplant le rayonnement UV et l’utilisation d’un photocatalyseur (TiO2) au sein d’un réacteur, est envisagé comme procédé de traitement tertiaire pour la désinfection des effluents dis secondaires. Les expérimentations photocatalytiques ont été réalisées sur une bactérie cible, E.coli. Elles ont été conduites en mode batch puis en mode continu. Les expérimentations en mode batch ont été réalisées sous irradiation contrôlée puis solaire. Les données expérimentales acquises sous irradiation contrôlée ont permis la comparaison des performances bactéricides de différents catalyseurs. Elles ont conduit en parallèle à la définition d’un modèle cinétique représentatif de la capacité bactéricide de chaque média. Les expérimentations solaires ont permis de valider le modèle cinétique sous irradiation solaire puis, d’étudier l’inactivation bactérienne dans un effluent réel. Par ailleurs, le potentiel bactéricide du traitement photocatalytique en régime permanent a été évalué. Le fonctionnement du procédé continu a été parfaitement décrit par un modèle cinétique se basant sur la loi cinétique initialement définie en mode batch. Finalement, l’inactivation d’E.coli a été évaluée par différentes techniques de quantification bactérienne. Cela a permit de mettre en évidence le mécanisme principal d’inactivation par voie photocatalytique, la lyse membranaire et d’apporter des informations sur l’état de viabilité « réel » des bactéries au cours du traitement photocatalytiqueThe study presented in this paper is part of the reuse of treated wastewater by advanced oxidation process (AOP), the heterogeneous photocatalysis. This process, coupling the UV radiation and the use of a photocatalyst (TiO2) in a reactor, is envisaged as tertiary treatment process for disinfection of said secondary effluent. Photocatalytic experiments were performed on a target bacterium, E. coli. They were conducted in batch and continuous mode. The experiments in batch mode were performed under controlled irradiation and sunlight. The experimental data obtained under controlled irradiation allowed the comparison of the bactericidal performance of different catalysts. They led in parallel to the definition of a representative kinetic model of the bactericidal capacity of each medium. Solar experiments were used to validate the kinetic model under solar irradiation and then to study the bacterial inactivation in a real effluent. Furthermore, the potential of the photocatalytic bactericidal treatment at steady state was evaluated. The operation of the continuous process has been thoroughly described by a kinetic model based on the kinetic law originally defined in batch mode. Finally, inactivation of E. coli was evaluated by different bacterial quantification techniques. This has made it possible to highlight the main mechanism of the photocatalytic bacterial inactivation, the membrane lysis. It provided information about the "real" state of the bacteria viability during the photocatalytic treatment
2
Pilavtepe, Mutlu. „High Hydrostatic Pressure Induced Inactivation Kinetics Of E. Coli O157:h7 And S. Aureus In Carrot Juice And Analysis Of Cell Volume Change“. Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12609205/index.pdf.
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The main objective of this study was to determine the pressure induced inactivation mechanism of pressure-resistant Escherichia coli O157:H7 933 and Staphylococcus aureus 485 in a low acid food.
Firstly, inactivation curves of pathogens were obtained at 200 to 400 MPa at 40ºC in peptone water and carrot juice. First-order and Weibull models were fitted and Weibull model described the inactivation curves of both pathogens more accurately than first-order model, revealing that food systems could exhibit either protective or sensitizing effect on microorganisms. Carrot juice had a protective effect on E. coli O157:H7 whereas it had a sensitizing effect on S. aureus, due to the naturally occurring constituents or phytoalexins in carrot roots that could have a toxic effect. Secondly, scanning electron microscopy (SEM) and fluorescent microscopy images of studied pathogens were taken. Developed software was used to analyze SEM images to calculate the change in the view area and volume of cells. Membrane integrity of pressurized cells was also examined using fluorescent microscopy images. The increase in average values of the view area and volume of both pathogens was significant for the highest pressure levels studied. The increase in volume and the view area could be explained by the modification of membrane properties, i.e., disruption or increase in permeability, lack of membrane integrity, denaturation of membrane-bound proteins and pressure-induced phase transition of membrane lipid bilayer. The change in volume and the view area of microorganisms added another dimension to the understanding of inactivation mechanisms of microbial cells by HHP.
3
Dehghan, Abnavi Mohammadreza Dehghan. „CHLORINE DECAY AND PATHOGEN CROSS CONTAMINATION DYNAMICS IN FRESH PRODUCE WASHING PROCESS“. Cleveland State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=csu1624196282479244.
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4
Klotz, Bernadette. „High hydrostatic pressure inactivation of Escherichia coli“. Thesis, University of Reading, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421204.
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5
Savant, Gaurav. „COMBINED OZONE AND ULTRAVIOLET INACTIVATION OF ESCHERICHIA COLI“. MSSTATE, 2003. http://sun.library.msstate.edu/ETD-db/theses/available/etd-07072003-191650/.
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The kinetics of Escherichia coli inactivation were studied using ultraviolet (UV) radiation, ozone, and UV and ozone (UVO) in combination in a batch reactor at varying pH levels (6, 7, and 8) and at a constant temperature of 25°C. The inactivation kinetics for all three treatment processes was pseudo first order, and the reaction rate constants were considered to be additive such that a combined reaction rate could be obtained by adding the kinetic rates of the processes applied and numerically small rates could be neglected in the computation of the combined rate. Statistical tests (ANOVA and student's t-test) performed on the inactivation data indicated no apparent effect of pH on the kinetics of the processes. It was found that the UVO process was the most efficient in inactivating E. coli. The increase in the inactivation rate with the UVO process is attributed to synergetic activity of UV and ozone which results in the generation of hydroxyl radicals from ozone decomposition.
6
Odeyemi, Babatunde O. „Hydrodynamic cavitation : effects of cavitation on inactivation of Escherichia coli (E.coli)“. Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/11009.
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7
Zhou, Xia 1953. „Inactivation of Escherichia coli and coliphage MS-2 by chloramine and copper“. Thesis, The University of Arizona, 1991. http://hdl.handle.net/10150/277945.
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The efficacy of chloramine in the presence of copper chloride was evaluated for the inactivation of an indicator bacteria Escherichia coli and coliphage MS-2. Both microorganisms were exposed to chloramine with and without copper chloride. Results showed an increase in the inactivation rate of Escherichia coli and MS-2 phage with an increasing concentration of chloramine. To achieve a 99 percent reduction in the number of Escherichia coli, an exposure of 46, 21, 6, and 5 minutes was necessary for 1, 2.5, 5, and 10 mg chloramine/L, respectively. A 99 percent reduction of MS-2 phage occurred after 60 and 25 minutes of exposure to 5 and 10 mg chloramine/L. Chloramine in the presence of copper increased the inactivation rate of Escherichia coli and MS-2 phage. The time needed for 99 percent inactivation of E. coli and MS-2 phage was reduced. Copper increases the inactivation rate of bacteria and viruses by chloramine. (Abstract shortened with permission of author.)
8
Moody, Vertigo. „Thermal inactivation kinetics of Escherichia coli and Alicyclobacillus acidoterrestris in orange juice“. [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0002222.
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9
Yan, Yuan. „Role of Intracellular Iron in Escherichia coli Inactivation by non-Thermal Processing“. The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316496149.
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10
Charoenwong, Duangkamol. „The investigation of mechanisms of inactivation of Escherichia coli by high hydrostatic pressure“. Thesis, University of Reading, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533739.
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Malone, Aaron S. „INACTIVATION MECHANISMS OF ALTERNATIVE FOOD PROCESSES ON ESCHERICHIA COLI O157:H7“. Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1237307369.
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Greene, Sarah Elisabeth. „Thermal Inactivation of Escherichia coli O157:H7 and Salmonella Agona in Wheat Flour“. Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/42521.
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Contaminated wheat flour has been identified as the probable vehicle of a multi-state outbreak of Escherichia coli O157:H7 associated with ready-to-bake cookie dough. Several cookie dough manufacturers are currently using heat-treated flour for ready-to-bake products, although data on thermal inactivation of foodborne pathogens in wheat flour remains scarce. The objective of this research was to first determine appropriate methods and parameters for bacterial inoculation and thermal treatment of wheat flour, and to subsequently determine the population reductions of E. coli O157:H7 and Salmonella Agona in artificially contaminated wheat flour following thermal treatment for 1, 5, 15 or 30 minutes at 55, 60, 65 or 70°C in a shaking water bath. Flour samples (aw = 0.55) in sterile plastic bags were individually inoculated (~109 CFU/g), pulsified to distribute cultures, and pressed to a uniform thickness (1mm) prior to heat treatment. Following treatment, samples were rapidly cooled and diluted with peptone water; then plated onto Tryptic Soy Agar (TSA) and incubated at 37°C for 24 h prior to enumeration. The minimum heat treatments required for a 5-log reduction in microbial populations (~ 109CFU/g to ~ 104CFU/g) were 5 minutes at 70°C and 30 minutes at 70°C for E. coli O157:H7 and S. Agona, respectively. This research supports the hypothesis that the microbiological safety of ready-to-bake products may be improved by the use of heat-treated flour.Master of Science in Life Sciences
13
Reed, Jennifer Leanne. „Model driven analysis of Escherichia coli metabolism“. Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2005. http://wwwlib.umi.com/cr/ucsd/fullcit?p3181789.
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Thesis (Ph. D.)--University of California, San Diego, 2005.Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed October 21, 2005). Vita. Includes bibliographical references (leaves 157-171).
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Wright, N. E. „Interrelation of the physiological status of Escherichia coli ATCC 8739 and its sensitivity towards chemical inactivation“. Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374563.
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Hyppólito, Marina Paz. „Efeitos da quitosana na inativação fotodinâmica de Escherichia coli“. Universidade Federal de Uberlândia, 2014. https://repositorio.ufu.br/handle/123456789/17425.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorChitosan is a functional material which offers unique characteristics as biocompatibility, biodegradability, atoxic, physiological inertness, antibacterial, chelating heavy metal ions, properties of gel formation, and hydrophilicity, and remarkable affinity for proteins. This study aimed to investigate the use of chitosan and additives, such as gold nanoparticles and photosensitizers, as alternative to inactivate microorganisms treatments. Chitosan of different brands were tested and characterized according to their structural properties in order to assess whether there are significant differences between the brands. The pH range of the acid solubilization of chitosan was varied and analyzed from tests of cell viability study of the antimicrobial properties of chitosan. The range of pH studies where there is no interference from acid in the results is at pH 5.0 and 6.5. Aggregation properties of chitosan and its interaction with bacteria were analyzed in the presence of gold nanoparticles, which became evident that the proposed method is simple, fast, effective and does not compromise the antimicrobial activity of chitosan. These experiments also showed a probable competition between colloidal gold and bacteria interaction with chitosan, but were also found a strong interaction between these materials. Other tests were performed with photosensitizers by assessing the interaction and possible synergism between materials improving the photoinactivation of microorganisms, but not verified or an intensification of the properties of the dyes and there was no effect of antimicrobial activity by chitosan.
A quitosana é um material funcional que oferece características únicas: biocompatibilidade, biodegradabilidade, atoxicidade, inércia fisiológica, propriedades antibacterianas, quelante de íons metálicos pesados, propriedades de formação de géis e hidrofilicidade, e notável afinidade com proteínas. Este trabalho teve como objetivo a investigação da utilização da quitosana e aditivos, tais como, fotossensitizadores e nanopartículas de ouro, como tratamentos alternativos para a inativação de micro-organismos. Quitosana de marcas comerciais diferentes foram testadas e caracterizadas segundo suas propriedades estruturais no intuito de avaliar se há diferenças significativas entre as marcas. A faixa de pH do ácido de solubilização da quitosana foi variada e analisada a partir de testes de viabilidade celular para estudo das propriedades antimicrobianas da quitosana. A faixa de estudos de pH onde não há interferência do meio ácido nos resultados é entre os pHs 5,0 e 6,5. Propriedades agregantes da quitosana e sua interação com bactérias foram analisadas na presença de nanopartículas de ouro, em que ficou evidente que a metodologia proposta é rápida, simples, eficaz e não compromete a atividade antimicrobiana da quitosana. Estes experimentos também mostraram uma provável competição entre ouro coloidal e bactérias em interagir com a quitosana, porém também foi constatada uma forte interação entre os materiais. Outros ensaios foram realizados com fotossensitizadores buscando avaliar a interação e possível sinergismo entre os materiais melhorando a fotoinativação de micro-organismos, mas não foi verificada uma intensificação das propriedades e em um dos corantes não houve efeito de atividade antimicrobiana pela quitosana.
Mestre em Química
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Amiali, Malek. „Inactivation of Escherichia coli O157:H7 and Salmonella enteritidis in liquid egg products using pulsed electric field“. Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85664.
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Pulsed Electric Field (PEF) processing, a novel, non-thermal food preservation method, has been shown to inactivate both spoilage and pathogenic microorganisms, while minimizing changes in the physical and organoleptic qualities of the food, such as those observed under conventional thermal processing. An understanding of the inactivation mechanisms and kinetics of microorganisms exposed to lethal or sub-lethal PEF treatments would allow industry and consumers to better understand and evaluate the potential of PEF technology as an alternative or complement to traditional methods of food preservation. This study consisted of three sets of experiments which sought to determine: (i) the electrical conductivity (EC) of various liquid food products (apple, orange and pineapple juices, egg white, whole egg and egg yolk) at different temperatures (5--55°C); (ii) the capacity of PEF (15 kV cm-1, 0°C) to inactivate Escherichia coli O157:H7 in dialyzed liquid egg products; and (iii) the effect of PEF (20 or 30 kV cm-1) in combination with temperature (10--40°C) on the inactivation of E. coli and Salmonella Enteritidis in liquid egg yolk (EY), whole egg (WE), or egg white (EW). The treatment chamber design was based in part on regression equations of EC vs. temperature developed in the first set of experiments. After only 0.1 sec of PEF (15 kV cm-1) treatment, l, 3 and 3.5 log reductions of E. coli were noted in dialyzed egg white, egg yolk and whole egg, respectively. Kinetic models of bacterial inactivation were proposed. A 210 mus exposure to PEF (30 kV cm-1 ) resulted in log reductions of 5.0 and 5.0 in egg yolk, 3.9 and 3.6 in WE and, 2.8 and 3.6 in egg white, for E. coli and S. Enteritidis, respectively. A maximum energy of 914 J was required to inactivate S. Enteritidis in WE. In egg white, cells injured by PEF represented 0.9 and 0.4 log for S. Enteritidis and E. coli, respectively. An exponential decay model and an Arrhenius equation were
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Rocha, Deisy Mara Gomes da Cruz. „Photodynamic inactivation of microrganisms with multicharged phythalocyanines“. Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14268.
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Mestrado em Biotecnologia - Biotecnologia Industrial e AmbientalThe main goal of this work was to synthesize and characterize new phthalocyanines (Pc) for the photodynamic inactivation of microorganisms. For this, the synthesis of a new family of zinc(II)Pc tetra- and octa- substituted at the peripheral positions was attempt. The compounds were characterized by mass spectrometry and NMR spectroscopy. The inactivation efficiency of six Zinc(II) Pc, tetra- octa- and hexadeca-substituted with DMAP groups was evaluated against a recombinant bioluminescent strain of Escherichia coli in its planktonic form. The experiments were carried out at a concentration of 20 μM of photosensitizer, and either red or white light, with a fluency rate of 150 mW cm-2 as energy source. Assays of photodynamic inactivation of biofilms of the bioluminescent strain were also conducted with red light and the PS that demonstrated better performance in the photodynamic inactivation of free cells. The generation of 1O2, the solubility, fluorescence quantum yield, photostability and cellular uptake were also assessed. Pc 4 and 5 presented the highest inactivation efficiency in the planktonic form of the bioluminescent E.coli, causing reductions of 4 log in their light emission. These molecules were however much less effective against biofilms of the same strain, causing reductions of approximately 2 log in the light emission. In conclusion, Pc 4 and 5 are promising photosensitizers for the photodynamic inactivation of planktonic E.coli, but it still necessary to find ideal conditions for the efficient inactivation of biofilms.
O objetivo deste trabalho foi sintetizar e caracterizar novas ftalocianinas (Pc) para serem testadas na inativação fotodinâmica de microrganismos. Nesse sentido tentou-se obter uma nova família de ftalocianinas de zinco(II) tetra e octa-substituídas nas posições periféricas. Os compostos foram caracterizados através de espectrometria de massa e espetroscopia de RMN. Foi avaliada a eficiência de inativação de seis zinco(II)Pc tetra- octa- e hexadeca- substituídas com grupos DMAP numa estirpe de Escherichia coli recombinante bioluminescente na sua forma planctónica. Os ensaios foram realizados a uma concentração de 20 μM de fotossensibilizador e luzes vermelha e branca com uma potência de 150 mW cm-2, como fontes de irradiação. Foram ainda realizados ensaios de inativação fotodinâmica de biofilmes da mesma estirpe bacteriana usando a luz vermelha e os PS que apresentaram melhores resultados nos ensaios com a forma planctónica. Foram também realizados testes de geração de 1O2, solubilidade, rendimento quântico de fluorescência, fotoestabilidade, estabilidade e uptake com as ZnPcDMAP. As Pc 4 e 5 apresentaram maior eficiência na inativação de E. coli na sua forma livre, causando reduções de 4 log na bioluminescência da bactéria. Contudo, mostraram reduzida eficiência na inativação fotodinâmica de biofilmes, causando reduções de apenas 2 log na bioluminescência. Em conclusão, Pc 4 e 5 são fotossensibilizadores promissores para a inativação fotodinâmica de E. coli na forma livre. No entanto, ainda é preciso encontrar as condições ideais para inativação mais eficiente de biofilmes.
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Black, Jennifer L. „The inactivation kinetics of Escherichia coli O157:H7 in beef, chicken and trout subjected to electron beam radiation under various temperatures, ionic strengths and water activities“. Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3982.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains vii, 59 p. : ill. Includes abstract. Includes bibliographical references (p. 56-58).
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Feist, Adam Michael. „Model-driven metabolic engineering of Escherichia coli a systems biology approach /“. Diss., [La Jolla] : University of California, San Diego, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3354731.
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Thesis (Ph. D.)--University of California, San Diego, 2008.Title from first page of PDF file (viewed June 2, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Yesil, Mustafa. „Enhancing the inactivation of Escherichia coli O157:H7 by bacteriophage and gaseous ozone to improve postharvest fresh produce safety“. The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1512103801957122.
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El, Zakhem Henri. „Inactivation des suspensions microbiennes de Saccharomyces cerevisiae et d’Escherichia coli par champs électriques pulsés modérés“. Compiègne, 2006. http://www.theses.fr/2006COMP1641.
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Les objectifs de ce travail sont d'étudier les effets de l'application des champs électriques pulsés modérés variant de 2 à 15 kV/cm sur les suspensions colloïdales d'E. Coli et de S. Cerevisiae. Le Tween 80 ainsi que les acides organiques sont ajoutés aux suspensions d'E. Coli pour étudier l'effet de leurs combinaisons au traitement CEP et un degré de destruction de 8 log est atteint. Le suivi de l'évolution de la conductivité durant le traitement des suspensions de S. Cerevisiae est utilisé pour suivre le degré de détérioration des cellules. Les données obtenues par le calcul de la conductivité sont en corrélation avec le comptage sur boîtes de Pétri. L'effet du CEP augmente avec le mélange des suspensions, l'augmentation de la température, l'ajout du surfactant et l'utilisation du traitement en continu. L'effet de la charge initiale en S. Cerevisiae est étudié et le phénomène de percolation est mis en évidence. La nature de l'agrégation est expliquée par les mesures du potentiel ∫The objectives of this study were to investigate the effects of moderate pulsed electric fields (2 to 7. 5 kV/cm) on colloidal suspensions of E. Coli and S. Cerevisiae. Tween 80 as well as organic acids were added to the E. Coli suspensions to study the effects of their combinations to the PEF, and a destruction degree of 8 log was reached. The electrical conductivity measurements during the PEF-treatment of S. Cerevisiae suspensions were used to monitor the extent of cell damages. Data obtained for the disintegration in conductivity experiments are found in good correlation with Petri dishes cultures counting. The PEF-induced lethality of the yeast cells increases with the mixing of suspensions, the increase of temperature, the adding of surfactant and the use of continuous treatment chamber. The effect of the yeast cells concentrations is studied and the percolation phenomenon is underlined. The nature of the enhanced aggregation was revealed by the ∫-potential measurements
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Middelberg, Anton Peter Jacob. „A model for the disruption of Escherichia coli by high-pressure homogenization /“. Title page, summary and contents only, 1992. http://web4.library.adelaide.edu.au/theses/09PH/09phm627.pdf.
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Martins, Leonardo Pedro Donas-Boto de Vilhena. „Stochastic model of transcription initiation of closely spaced promoters in escherichia coli“. Master's thesis, Faculdade de Ciências e Tecnologia, 2011. http://hdl.handle.net/10362/7009.
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Dissertação para obtenção do Grau de Mestre
em Engenharia BiomédicaThe regulatory mechanisms of transcription allow organisms to quickly adapt to changes in their environment and often act during transcription initiation. Here, a stochastic model of transcription initiation at the nucleotide level is proposed to study the dynamics of RNA production in closely spaced promoters and their regulatory mechanisms. We study how different arrangements (convergent e divergent), distance between transcription start sites (TSS), and various kinetic parameters affect the dynamics of RNA production. Further, we analyze how the kinetics of various steps in transcription initiation can be regulated by varying locations of repressor binding sites. From the results, we observe that the rate limiting steps have strong influence in the kinetics of RNA production. We find that interferences between RNA polymerases in divergent overlapped and convergent geometries causes the distribution of time intervals between the production of consecutive RNA molecules from each TSS to increase in mean and standard deviation, which leads to stronger fluctuations in the temporal levels of RNA molecules. We observe that small changes in the distance between TSSs can lead to abrupt transitions in the dynamics of RNA production, particularly when this change changes the geometry from overlapped to non-overlapped promoters. From the study of the correlation in the choices of directionality and on the time series of RNA productions we show that by tuning the distances and directions of the two TSS one can obtain both negative and positive correlations. We further show that distinct repression mechanisms of transcription initiation in steps such as the open and closed complex formation and promoter escape have different effects on the dynamics of RNA production. The study of these models will help the study of how genetic circuits have evolved and assist in designing artificial genetic circuits with desired dynamics.
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Ghazi, Alexandre. „La lactose perméase d'Escherichia coli : cotransport proton lactose et théorie chimiosmotique localisée, inactivation in vivo de la protéine“. Paris 11, 1987. http://www.theses.fr/1987PA112307.
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Le lactose perméase d’E. Coli est une protéine membranaire qui catalyse le transport actif du lactose en symport avec un proton. Le travail présenté ici comporte deux parties distinctes correspondant à des thèmes utilisant tous deux le lactose perméase comme système expérimental. La théorie chimiosmotique, dans sa formation initiale (dite délocalisée), est en contradiction, au moins apparente, avec un certain nombre de tests expérimentaux. Parmi ceux-ci, ceux qui traitent des relations flux-force sont les plus contraignants. La validité de ce test a néanmoins été remise en cause récemment dans un cas particulier. Nous examinons d’abord, au plan théorique, le bien-fondé de cette critique. Au plan expérimental, l’étude des relations flux-force en bioénergétique a jusqu’ici concerné uniquement la phosphorylation oxydative et phosphorylation, il n’existe pas de relation unique entre le flux (ici vitesse de transport du lactose catalysé par le lactose perméase) ou accumulation d’une part, et force (force promotrice) d’autre part. Ce résultat est compatible avec un mécanisme chimiosmotique localisé. Nous avons mis en évidence un phénomène d’inactivation du lactose perméase in vivo (dans la membrane). Les caractéristiques au niveau de la perméase ainsi que les conditions de cette inactivation sont décrites. On montre en particulier que ce phénomène met en jeu l’activité de la chaine respiratoire d’E. Coli et certaines protéases. L’inactivation du lactose perméase pourrait refléter un mécanisme physiologique
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Kasler, David R. „Effects of Moderate Electric Field Plus Heat Pretreatment on Bacterial Inactivation in Whole Shell Hen Eggs by Ozone“. The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1434445830.
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Faure, Marie. „Purification de l'air ambiant par l'action bactéricide de la photocatalyse“. Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL076N/document.
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Cette étude s’inscrit dans le cadre de l’amélioration des connaissances sur la dégradation photocatalytique des bioaérosols bactériens. La photocatalyse est une technique d’épuration basée sur l’excitation d’un semi-conducteur par un rayonnement le plus généralement ultraviolet. Cette technologie permet, en théorie, de minéraliser pas à pas les polluants. Or, si les conditions optimales ne sont pas réunies, la minéralisation incomplète peut conduire à des sous-produits de dégradation de toxicité potentiellement préoccupante.L’objectif de ces travaux a donc été d’apporter des éléments de compréhension quant aux mécanismes de dégradation photocatalytique d’un bioaérosol bactérien modèle d’E.coli, où de nombreux phénomènes sont couplés. Ainsi, pour distinguer les différents processus mis en jeu, deux approches expérimentales ont été menées. La première, nommée approche « batch », a permis d’isoler la réaction photocatalytique, à proprement parler, en étudiant les étapes d’inactivation, de libération de sous-produits et de minéralisation progressive. La seconde, appelée approche « dynamique » a permis quant à elle la mise en place d’un dispositif expérimental adapté à la dégradation photocatalytique d’un bioaérosol d’E.coli. Les capacités de la photocatalyse à inactiver et minéraliser des espèces bactériennes ont pu être démontrées. Les paramètres clés d’une dégradation efficace ont été mis en évidence et ont permis de décrire les verrous indispensables à une industrialisation sûre du procédéThis study comes within the scope of improving knowledge concerning the photocatalytic degradation of bacterial bioaerosol. Photocatalysis is a purification technology generally based on the excitation of a semiconductor by an ultraviolet radiation. This technology can, in theoretical ways, mineralize pollutants step by step. However, if optimal conditions are not gathered, this mineralization is incomplete and can lead to the formation of potentially toxic by-products. The aim of this work was therefore a better understanding of the mechanisms of photocatalytic degradation of a bacterial bioaerosol of E.coli, where numerous phenomenon are linked. Thus, to distinguish the different processes, two experimental approaches were used. The first one, called “batch approach”, allowed to consider the photocatalytic reaction itself, by studying the steps of inactivation, by-products formation and progressive mineralization. The second one, named “dynamic approach”, consisted to design an experimental setup suited to the photocatalytic degradation of a bioaerosol of E.coli. The abilities of photocatalysis to inactivate and mineralize bacteria could be demonstrated. The key parameters of an efficient degradation were highlighted and allowed to underline the problems to solve before having a safe industrialization of the photocatalysis
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Soini, J. (Jaakko). „Effects of environmental variations in Escherichia coli fermentations“. Doctoral thesis, Oulun yliopisto, 2012. http://urn.fi/urn:isbn:9789514299360.
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Abstract Production of recombinant proteins and organic molecules by microbial fermentation is a widely used process in pharmaceutical, biofuel, food and chemical industries. Micro-organisms are cultivated in a bioreactor enabling a proper environment and conditions for production of the desired product molecule. Usually, however, the conditions in the bioreactor are inhomogeneous because of technical limitations such as insufficient mixing. This causes gradients in various parameters such as temperature, ph, dissolved oxygen or substrate concentration, which can have a negative effect on product quality and quantity. Understanding the effects of such environmental variations for the host organism and product molecule are crucial for the bioprocess control. The aim of this dissertation was to study the metabolic and gene expression level response of Escherichia coli bacterium for variating conditions in the bioreactor. The responses for rapid temperature increase and oxygen limitation was studied by shift experiments. The effect of oscillating oxygen and glucose concentrations, typical for industrial scale processes, was studied with a scale-down model. The main results were obtained in the oxygen downshift experiments. It was shown that a non-canonical amino acid norvaline, known to replace leucine in recombinant proteins, is accumulated in significant concentration under oxygen limitation. The accumulation of norvaline was also observed in the scale-down model indicating that norvaline could also be found in large scale processes. The quantitative gene expression results for the norvaline pathway genes showed no clear response. This indicates that the norvaline formation occurs due to the changes on metabolic rather than transcriptional level. The second key result of this dissertation was the finding, that the accumulation of formate, a typical anaerobic metabolite, was diminished by medium boosted with trace amounts nickel, selenium and molybdenum, enabling the activity of formate degrading enzyme complex. The results of this dissertation can be utilized in the industrial process optimisation and as a basis for further bioprocess studiesTiivistelmä Vierasproteiinien ja orgaanisten molekyylien tuottaminen fermentoimalla on paljon käytetty menetelmä lääke-, bioenergia-, elintarvike- sekä kemianteollisuudessa. Mikrobit kasvatetaan bioreaktorissa, joka mahdollistaa sopivan kasvuympäristön ja tuotanto-olosuhteet halutulle tuotteelle. Usein bioreaktorin olosuhteet ovat kuitenkin epätasaiset teknisten rajoitteiden kuten riittämättömän sekoitustehon vuoksi. Tämä aiheuttaa eri muuttujien, kuten happi- ja ravinnepitoisuuden, pH:n tai lämpötilan vaihtelua ajan ja paikan suhteen, millä voi olla haitallinen vaikutus tuotteen laatuun tai saantoon. Ympäristötekijöiden muutosten isäntäsolulle tai tuotemolekyylille aiheuttamien vaikutusten ymmärtäminen ovat yksi ratkaisevista tekijöistä bioprosessien hallinnassa. Tässä väitöskirjassa tutkittiin Escherichia coli -bakteerin aineenvaihdunnan sekä geeniekspression vasteita bioreaktorin ajan ja paikan suhteen vaihtelevissa olosuhteissa. Hapenpuutteen ja lämpötilan nousun vaikutusta tutkittiin kokeilla, joissa olosuhdetta kertaluontoisesti ja nopeasti muutettiin. Teollisille fermentointiprosesseille tyypillistä happi- ja ravinnepitoisuuksien jatkuvaa vaihtelua tutkittiin suurta bioreaktoria jäljittelevällä pienoismallilla. Tärkeimmät tulokset liittyivät kokeisiin, joissa tutkittiin hapenpuutetta. Kokeissa kävi ilmi, että happirajoitetuissa olosuhteissa muodostuu huomattavia määriä epätavallista aminohappoa norvaliinia, jonka tiedetään korvaavan leusiinia vierasproteiineissa. Norvaliinin muodostumista havaittiin myös pienoismallilla tehdyissä kasvatuksissa, osoittaen että norvaliinia voi mahdollisesti löytyä myös suuren mitan prosesseista. Geeniekspressiomittaukset eivät osoittaneet muutoksia norvaliinin aineenvaihduntareitillä, osoittaen että havaittu norvaliinin muodostuminen tapahtuu aineenvaihdunnallisten muutosten seurauksena. Toinen tässä väitöstutkimuksessa saatu tärkeä tulos oli muurahaishapon kertymisen vähentyminen, kun kasvatusliuokseen lisättiin nikkeliä, seleeniä ja molybdeeniä aktivoimaan muurahaishappoa hajottavaa entsyymikompleksia. Tämän väitöstutkimuksen tuloksia voidaan hyödyntää teollisten prosessien optimoinnissa ja perustana uusille tutkimusaiheille
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Nair, Bindu. „Delineating a topological model for a functional and export-competent escherichia coli siderophore receptor, FEPA“. free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9924909.
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Santos, Renata Oliveira. „Estudo da inativação fotodinâmica de Escherichia coli em água utilizando azul de metileno e rosa de bengala“. Universidade Federal de Uberlândia, 2014. https://repositorio.ufu.br/handle/123456789/17406.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThis work aimed to develop a procedure for disinfecting water by photodynamic inactivation of microorganisms and subsequent removal of photosensitizers. The Escherichia coli photoinactivation was performed using PHLS (Policromatic Halogen Light System) light system irradiation, Methylene Blue and Rose Bengal as photosensitizers, cationic and anionic dyes , respectively. The phase separation between the photosensitizers and the analyzed sample was studied by coagulation, being used the crushed seeds of Moringa oleifera, Chitosan powder and commercial Aluminum Sulphate. All experiments were performed previously in samples of E. coli (ATCC 25922) prepared with a turbidity of about 01 on the Mac Farland scale and later in a sample of effluent from the Sewage Treatment Plant of Uberlândia - MG. The results were quite significant as much photoinactivation as the photosensitizers removal, being Moringa oleifera the best coagulant used, able to remove, from effluent sample, 96.9% Rose Bengal and 75.9% Methylene Blue, both at a concentration of 3,91x10-5 mol L-1.
O presente trabalho visou desenvolver um procedimento para a desinfecção de águas através da inativação fotodinâmica de micro-organismos e posterior remoção dos fotossensitizadores. A fotoinativação de Escherichia coli foi realizada utilizando sistema de irradiação luminosa PHLS (Policromatic Halogen Light System) e Azul de Metileno e Rosa de Bengala como fotossensitizadores, corantes catiônico e aniônico, respectivamente. A separação de fases entre os fotossensitizadores e a amostra analisada foi estudada através de coagulação, sendo utilizadas as sementes de Moringa oleífera trituradas, Quitosana em pó e Sulfato de alumínio comercial. Todos os experimentos foram realizados previamente em amostras de E. coli (ATCC: 25922) preparadas com turvação de aproximadamente 01 na escala de Mac Farland e posteriormente em amostra de efluente proveniente da Estação de Tratamento de Esgoto de Uberlândia - MG. Os resultados obtidos foram bastante expressivos tanto na fotoinativação, quanto na remoção dos fotossensitizadores, sendo a Moringa oleífera o melhor coagulante utilizado, tendo conseguido remover da amostra de efluente 96,9% do Rosa de Bengala e 75,9% do Azul de Metileno, ambos em uma concentração de 3,91x10-5 mol L-1.
Mestre em Química
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Yesil, Mustafa. „EFFICACY OF GASEOUS OZONE IN COMBINATION WITH VACUUM COOLING AND PRE-WASHING FOR THE INACTIVATION OF Escherichia coli O157:H7 ON FRESH PRODUCE“. The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1331148507.
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Svensson, Marie. „The temperature-limited fed-batch technique for control of Escherichia coli cultures“. Doctoral thesis, Stockholm : School of Biotechnology, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4154.
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Zhi, Xiaoduo. „Transcription-Coupled DNA Supercoiling in Escherichia Coli: Mechanisms and Biological Functions“. FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/865.
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Transcription by RNA polymerase can induce the formation of hypernegatively supercoiled DNA both in vivo and in vitro. This phenomenon has been explained by a “twin-supercoiled-domain” model of transcription where a positively supercoiled domain is generated ahead of the RNA polymerase and a negatively supercoiled domain behind it. In E. coli cells, transcription-induced topological change of chromosomal DNA is expected to actively remodel chromosomal structure and greatly influence DNA transactions such as transcription, DNA replication, and recombination.
In this study, an IPTG-inducible, two-plasmid system was established to study transcription-coupled DNA supercoiling (TCDS) in E. coli topA strains. By performing topology assays, biological studies, and RT-PCR experiments, TCDS in E. coli topA strains was found to be dependent on promoter strength. Expression of a membrane-insertion protein was not needed for strong promoters, although co-transcriptional synthesis of a polypeptide may be required. More importantly, it was demonstrated that the expression of a membrane-insertion tet gene was not sufficient for the production of hypernegatively supercoiled DNA. These phenomenon can be explained by the “twin-supercoiled-domain” model of transcription where the friction force applied to E. coli RNA polymerase plays a critical role in the generation of hypernegatively supercoiled DNA.
Additionally, in order to explore whether TCDS is able to greatly influence a coupled DNA transaction, such as activating a divergently-coupled promoter, an in vivo system was set up to study TCDS and its effects on the supercoiling-sensitive leu-500 promoter. The leu-500 mutation is a single A-to-G point mutation in the -10 region of the promoter controlling the leu operon, and the AT to GC mutation is expected to increase the energy barrier for the formation of a functional transcription open complex. Using luciferase assays and RT-PCR experiments, it was demonstrated that transient TCDS, “confined” within promoter regions, is responsible for activation of the coupled transcription initiation of the leu-500 promoter. Taken together, these results demonstrate that transcription is a major chromosomal remodeling force in E. coli cells.
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George, Bruce Lee. „A computer model of the L-arabinose gene-enzyme complex of E. coli with an analysis of its control methodology /“. The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487263399022861.
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Rodriguez, Rodriguez Mauricio. „Pyrimidine nucleotide de novo biosynthesis as a model of metabolic control“. Texas A&M University, 2005. http://hdl.handle.net/1969.1/4425.
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This manuscript presents a thorough investigation and description of metabolic control
dynamics in vivo and in silico using as a model de novo pyrimidine biosynthesis.
Metabolic networks have been studied intensely for decades, helping develop a detailed
understanding of the way cells carry out their biosynthetic and catabolic functions.
Biochemical reactions have been defined, pathway structures have been proposed,
networks of genetic control have been examined, and mechanisms of enzymatic activity
and regulation have been elucidated. In parallel with these types of traditional
biochemical analysis, there has been increasing interest in engineering cellular
metabolism for commercial and medical applications. Several different mathematical
approaches have been developed to model biochemical pathways by combining
stoichiometric and/or kinetic information with probabilistic analysis, or deciphering the
comparative logic of metabolic networks using genomic-derived data. However, most of
the research performed to date has relied on theoretical analyses and non-dynamic
physiological states. The studies described in this dissertation provide a unique effort
toward combining mathematical analysis with dynamic transition experimental data.
Most importantly these studies emphasize the significance of providing a quantitative framework for understanding metabolic control. The pathway of de novo biosynthesis of
pyrimidines in Escherichia coli provides an ideal model for the study of metabolic
control, as there is extensive documentation available on each gene and enzyme involved
as well as on their corresponding mechanisms of regulation. Biochemical flux through
the pathway was analyzed under dynamic conditions using middle-exponential growth
and steady state cultures. The fluctuations of the biochemical pathway intermediates and
end products transitions were quantified in response to physiological perturbation.
Different growth rates allowed the comparison of rapid versus long-term equilibrium
shifts in metabolic adaptation. Finally, monitoring enzymatic activity levels during
metabolic transitions provided insight into the interaction of genetic and biochemical
mechanisms of regulation. Thus, it was possible to construct a robust mathematical
model that faithfully represented, with a remarkable predictability, the nature of the
metabolic response to specific environmental perturbations. These studies constitute a
significant contribution to the fields of quantitative biochemistry and metabolic control,
which can be extended to other cellular processes as well as different organisms.
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Thiele, Ines. „A stoichiometric model of Escherichia coli 's macromolecular synthesis machinery and its integration with metabolism“. Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3355081.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed June 16, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 209-232).
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Emiola, Akintunde. „A model for the regulation of lipopolysaccharide synthesis during outer membrane biogenesis in Escherichia coli“. Thesis, University of East London, 2015. http://roar.uel.ac.uk/4802/.
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The role of systems biology in the interpretation and analysis of important biological events is gaining rapid acceptance in a number of biological fields. Here a computational systems approach was applied to investigate the production and regulation of Escherichia coli’s (E. coli) outer membrane. The outer membrane comprises of phospholipids in the inner leaflet, and lipopolysaccharides (LPS) in the outer leaflet. LPS is an endotoxin that elicits a strong immune response from humans and its biosynthesis is in part, regulated via degradation of LpxC and WaaA enzymes by the protease FtsH. Despite a substantial amount of research conducted on LPS synthesis, there is remarkably little information on its regulation. The model of the outer membrane synthesis was completed in two phases; firstly a model of lipid A (representing the LPS pathway) was constructed followed by an integrated pathway model which incorporated fatty acids biosynthesis pathway (representing phospholipid production). The parameters used to construct the model were derived from published datasets where available, and estimated when necessary prior to model fitting. Model validation was carried out using a combination of published datasets alongside subsequent experimental data from this research. Model findings suggested that the FtsH-mediated LpxC degradation signal arises from levels of lipid A disaccharide, the substrate for LpxK. This was subsequently validated experimentally using an lpxK overexpression system. Analysis of the integrated model further refined this mechanism indicating the catalytic activity of LpxK appears to be dependent on the concentration of unsaturated fatty acids. This is biologically important because it assists in maintaining LPS/phospholipids homeostasis. Further crosstalk between the fatty acids and lipid A biosynthetic pathways was revealed by experimental observations that LpxC is additionally regulated by an unidentified protease whose activity is independent of lipid A disaccharide concentration, but could be induced in vitro by palmitic acid. The biological relevance of this acute mechanism is not obvious; however, experiments aimed at causing abrupt damage to the cell wall or membrane (by antimicrobials) suggest that under conditions which directly damage membrane structure, LPS regulation via this unidentified protease may be crucial. Computational analysis into the regulation of WaaA suggested that its proteolytic regulation does not affect the LPS synthetic rate. Subsequent experimental analysis provided evidence that WaaA regulation is aimed at controlling the quality of LPS synthesized by preventing glycosylation of undesirable lipid acceptors. Overexpression of waaA resulted in increased levels of 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) sugar whereas, levels of heptose were not elevated in comparison to non-overexpressed cells. This implies that an uncontrolled production of WaaA does not increase LPS level but rather re-glycosylates lipid A precursors. This is the first time experimental data has been produced attempting to explain the regulation of WaaA. Computation of flux coefficient indicates that LpxC is the rate-limiting step when pathway regulation is ignored, but LpxK becomes the limiting step if feedback regulation is included as it is in vivo. Thus, in contrast to LpxC, LpxK may represent a more appropriate target for novel drug development. Overall, the findings of this work provide novel insights into the complex biogenesis of the E. coli outer membrane.
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Redfearn, James C. „A Comprehensive Model of the Structure and Function of the FtsZ Ring of Escherichia coli“. Kent State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=kent1460475643.
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Bandla, Srinivasarao. „Design of Dean flow Ultraviolet (UV) reactors and testing their efficacy for inactivation of Escherichia coli W 1485 and Bacillus cereus spores in milk“. OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/382.
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Consumer demand for fresher foods has necessitated the use of non-thermal technologies in processing milk. Two Dean Flow UV reactors (1/16" ID × 1/32" Thick & 1/8" ID × 1/32" Thick) were designed in the laboratory. The objective of this study was to examine the efficacy of designed UV reactors at four levels of Reynolds numbers (Re) on inactivation of Escherichia coli W 1485 cells and Bacillus cereus spores in raw cow milk (RCM), commercially processed skimmed cow milk (SCM) and raw soymilk (RSM). RCM, SCM and RSM were inoculated separately with E. coli W 1485 and B. cereus spores and were treated through the designed reactors for a residence time of 11.3 ± 0.1 s, equivalent to an UV dose of 0.05 J/ml in 1/16" ID reactor and 0.02 J/ml in 1/8" ID reactor. Four levels of Re were tested in the range of 181-1372. The influence of tube diameter (thickness of milk exposed to UV) and Re (indicator of turbulence) at constant residence time (11.3 ± 0.1 s) on inactivation of both the bacteria in both the UV reactors was analyzed using two-way ANOVA with proc GLM in SAS software. E. coli was inactivated to non-detectable levels (≥7.8 log10 CFU/ml) in SCM from the second level of Re (532.2) in 1/16" ID reactor. E. coli was also inactivated significantly (> 5logs) in RSM at the highest Re (1372) but this was not achieved in the case of RCM (712.7). Increasing the residence time to 14.2 s or greater (17 s) (equal to UV dose of 0.06 and 0.08 J/ml) inactivated E. coli cells to non-detectable levels in RCM using 1/16" ID reactor at the highest level of Re (712.7). Reduction of E. coli cells were in the range of 0.45-7.78 logs whereas B. cereus spores were in range of 1.06- 3.29 logs in all types of milk used in this study. The interaction effect of tube diameter and Re was statistically significant for E. coli cells in RCM, and SCM; B. cereus spores in SCM, and RSM (p < 0.05) whereas this was statistically non significant for E. coli cells in RSM and B. cereus spores in RCM (p > 0.05). Main effects of Reynolds number, and tube diameter were statistically significant (p < 0.05) on inactivation of B. cereus spores in RCM and E. coli cells in RSM. Inactivation efficiencies for both bacteria were higher in 1/16" ID reactor than 1/8" ID reactor. Using the 1/16" ID reactor at highest level of Re (RCM Re = 712.7, RSM Re = 1372), inactivation of standard plate count (SPC) present in RSM and RCM, and lipid oxidation during storage period (0, 1, 3 and 7 days) were measured. Inactivation of SPC in UV-treated RSM (3 logs) was lower than thermal pasteurization at 72°C for 20 s (7 logs). In case of RCM, the SPC was inactivated to 1.9 logs from 4.2 logs. Sensory evaluation (olfactory) of UV treated, untreated (milk passed through the 1/16" ID reactor while the UV lights turned off), and fresh RCM (control) suggested no change in flavor after treatment and upto 1 day after storage in refrigerated condition, but a perceivable change in the quality of UV treated and untreated cow milk were observed during the 3rd and 7th days when compared with fresh RCM (milked same day). RCM was treated with different UV dose levels (0.04, 0.05, 0.08, 0.12 and 0.16 J/ml) to examine the effect of UV light on malondialdehyde and other reactive substances using TBARS test kit. Reactive substances such as malondialdehyde content increased as the UV dose increased. The presence of malondialdehyde and other reactive substances were not significantly different (p < 0.05) in both thermal and UV-pasteurized soymilk; whereas these substances were found to be higher in UV-treated RCM after 7 days of storage than the untreated milk stored for 7 days at 4 °C and the fresh RCM. The designed reactors 1/16" ID and 1/8" ID reactors were useful to inactivate bacteria present in milk. But, the inactivation efficiency was more in 1/16" ID reactor than 1/8" ID reactor.
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Lee, Jaesung. „Calorimetric and microbiological evaluation of bacteria after exposure to food preservation treatments“. Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1078597088.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xvi, 231 p.; also includes graphics (some col.) Includes bibliographical references (p. 212-224). Available online via OhioLINK's ETD Center
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Cameron, Gemeia. „Synthesis, characterizaton, and effects of silver impregnated alumina on escherichia coli as a model for antimic Systhesis, characterization, and effects of silver impregnated alumina on escherichia coli as a model for antimicrobial control of gram-negative bacteria“. DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2010. http://digitalcommons.auctr.edu/dissertations/195.
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The recognition of the anti-microbial activity of oligodynamic metals such as silver has been a basis for the development of many antimicrobial processes and products. More specifically, silver and silver salts have been widely employed, particularly in water disinfection. Nano-sized silver particles have numerous commercial applications, including disinfection of water, food processing and disinfection of healthcare equipment. In Escherichia coli, which are vulnerable to silver, it has been suggested that the lipopolysaccharides on their surface contain high affinity binding sites for divalent cations. It has been shown that silver interacts with the cell membranes of bacteria, which alters their mesosomal functions, such as their ability to aid DNA replication. The nature of the bactericidal activity of silver and even more specifically silver impregnated alumina, its mechanistic details, and properties that influence disinfection are poorly understood. However, we hypothesize that silver impregnated alumina is an effective antimicrobial agent that could be used to improve water quality. To study this hypothesis, E. coil was exposed to various concentrations of metallic silver, impregnated on the surface of alumina and silver impregnated alumina’s effect in compromising bacterial cellular viability was determined. These studies reveal that E. coli exposure to concentrations of silver impregnated alumina results in decreased bacteria viability. Additionally, when calcination temperature and time are increased, a more effective catalyst is produced for antimicrobial activity. These studies also show that the silver impregnated alumina ability to kill bacteria is dose dependent, and that silver adsorption occurs upon contact with bacteria. Further, these studies show that silver is the active agent within the silver-alumina catalyst. Based upon this data, we believe that silver impregnated alumina is a more effective antimicrobial agent than silver nitrate solution.
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Korkmaz, Erdural Beril. „Photocatalytic Antimicrobial And Self-cleaning Properties Of Titania-silica Mixed Oxide Thin Films“. Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615137/index.pdf.
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In this study photocatalytic antibacterial and self-cleaning activities of TiO2-SiO2 thin films as a function of TiO2/SiO2 ratios were investigated. TiO2-SiO2 mixed oxides were synthesized by sol-gel method and coated over soda-lime glass plates by dip coating technique. Escherichia coli was used as a model microorganism for the photocatalytic antibacterial tests. Degradation rate of methylene blue (MB) molecules was used to characterize photocatalytic self-cleaning activities of thin film surfaces.
The maximum antibacterial activity was achieved over 92 wt% SiO2 containing thin films. However, when the SiO2 content exceeds 92 wt%, photocatalytic antibacterial activity decreased considerably, which was explained by the dilution of TiO2 phase and inaccessibility of TiO2. Increase in photocatalytic antibacterial activity was attributed to increases in the relative surface area, roughness, hydroxyl (OH-) groups and bacterial adhesion. The favored bacterial adhesion enhanced direct contact of bacteria with TiO2 particles and surface reactive oxygen species.
The highest initial decomposition rate of MB was obtained for 60 wt% SiO2 and the activity decreases as SiO2 concentration increases. The increase in photocatalytic activity by the SiO2 addition can be explained by the increase of the amount of MB per unit area of TiO2-SiO2 thin films.
Different adsorption capability of thin films against MB molecule and E. coli cell was explained as the first reason why the antibacterial and self-cleaning activities reached their maximum values at different SiO2 ratios. The second reason could be related with the different control mechanisms of self-cleaning and antibacterial activities by different textural and surface properties.
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Amaral, Larissa Souza. „Otimização da inativação fotodinâmica de E. coli por fotossensibilizadores veiculados por nanopartículas de sílica“. Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/82/82131/tde-22062016-105849/.
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A nanotecnologia tem sido aplicada para o desenvolvimento de materiais para diversas aplicações inclusive na inativação de patógenos. As nanopartículas de sílica (npSi) destacam-se pela alta área superficial, facilidade na alteração da superfície para aumento da eficiência adsortiva, penetrabilidade e toxicidade para bactérias gram-negativas sendo biocompatíveis para células de mamíferos e mais foto-estáveis que a maioria dos compostos orgânicos. Devido as suas vantagens, as npSi podem ser usadas para veicular fotossensibilizadores (FSs) uma vez que permitem sua utilização em solução aquosa em que os FSs geralmente são insolúveis. Além disso, o uso de FSs em vez de antibióticos, permite a inativação microbiológica pela Terapia Fotodinâmica sem que as bactérias adquiram resistência por mecanismos genéticos. Esse processo ocorre pela interação entre um FS, luz e oxigênio molecular produzindo oxigênio singleto que é extremamente reativo danificando estruturas celulares. O objetivo desse estudo foi otimizar a fotoinativação dinâmica de E .coli utilizando Azul de Metileno (AM) e Azul de Toluidina O (ATO) veiculados por npSi. As npSi foram preparadas pela metodologia sol-gel, caracterizadas por microscopia eletrônica de varredura (MEV) e submetidas à adsorção de AM e ATO em sua superfície. A presença de AM e ATO na superfície das npSi foram analisadas por espectroscopia no infravermelho; espectroscopia de fluorescência por raio-X e análise termogravimétrica. O planejamento experimental, iniciado pelo fatorial 23 e modelado ao composto central em busca das condições ótimas foi adotado pela primeira vez nessa aplicabilidade, visando a fotoinativação de E. coli empregando AM e ATO em solução e em seguida com npSi. AM e ATO veiculados por npSi permitem a fotoinativação em concentrações mais baixas de FS (20 e 51% respectivamente), causando desestruturação da integridade bacteriana demonstrada por MEV. Os resultados sugerem que a veiculação de AM e ATO por npSi é extremamente efetiva para a fotoinativação dinâmica de E. coli e que o planejamento composto central pode levar à completa inativação das bactérias.Nanotechnology has been applied to the development of materials for several apllications inclusive inactivation of pathogens. The silica nanoparticles (npSi) are distinguished by high surface area, ease of change the surface in order to increase the adsorption efficiency, penetrability and toxicity in gram-negative bacteria being biocompatible with mammalian cells and more photo-stable than most the organic compounds. Due to its advantages, npSi can be used to carry photosensitizers (PSs) since they allow its use in aquous solution in which PSs are frequently insoluble. Furthermore, the use of PSs instead of antibiotics, allows the microbiological inactivation by Photodynamic Therapy without bacteria to develop resistance by genetic mechanisms. This process occurs by the interaction among a PS, light and molecular oxygen producing singlet oxygen, which is extremely reactive, causing damage to cellular structures. The aim of this study was to optimize the photoinactivation of E. coli using Methylene Blue (MB) and Toluidine Blue O (TBO) carried by npSi using the central composite design. The npSi were prepared by sol-gel method, characterized by scanning electron microscopy (SEM) and subjected to adsorption of MB and TBO on its surface. The presence of FSs on the surface of npSi were analyzed by infrared spectroscopy, fluorescence X-ray spectroscopy and thermogravimetric analysis. The experimental design, initiated by the factorial 23 and modeled by the central composite in search of the optimal conditions was adopted for the first-time for this applicability, aiming the E. coli photoinactivation employing MB and TBO in solution and then with npSi. MB and TBO carried by npSi allowed the photoinactivation in lower concentrations of PS (20 and 51% respectively), causing disruption of bacterial integrity demonstrated by SEM. The results suggest that MB and TBO carried by npSi are extremely effective for dynamic photoinactivation of E. coli and the central composite design can lead to complete inactivation of bacteria.
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Potapow, Andre. „Investigation of mammary blood flow changes by transrectal colour Doppler sonography in an Escherichia coli mastitis model“. Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-120814.
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Gardner, Stewart G. „Studies of PhoU in Escherichia coli: Metal Binding, Dimerization,Protein/Protein Interactions, and a Signaling Complex Model“. BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/5685.
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Phosphate is an essential nutrient for all forms of life. Escherichia coli has a PhoR/PhoB two component regulatory system that controls the expression of various genes whose products allow the cell to thrive in low phosphate environments. The signaling mechanism of the PhoR/PhoB system has been studied and the phosphorylation cascade that controls gene expression is well understood. What is still unknown is how PhoR senses the phosphate level of the environment. The PstS, PstC, PstA, PstB, and PhoU proteins play a role in this signal sensing. This work confirms the hypothesis that the PstSCAB complex senses the environmental phosphate and that phosphate signal is passed through PhoU to PhoR. Further, this work characterizes residues important for interaction on PhoU and PhoR and identifies a structural model for interaction. This model points to a potential mechanism for PhoU mediated signaling to PhoR. We tested this model with direct coupling analysis and obtained further confirmation. Further use of these techniques may elucidate more of the interactions necessary for proper phosphate signaling.
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Reding, Roman Rafael Carlos. „Ecological conditions leading to the seep of antibiotic resistance genes in the model-type bacterium Escherichia coli“. Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/19693.
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In antibiotic therapy design, conventional wisdom holds that higher antibiotic dosages always leads to the observation of fewer bacterial cells, resulting in a monotonic decay in cell number as a function of increasing antibiotic dose; accordingly, throughout this thesis, we will call this phenomenon a monotone dose-response profile. When we analysed the evolution of antibiotic resistance mediated by the multi-drug efflux pump AcrAB-TolC in Escherichia coli to study if such a monotone dose-response is maintained at all times, our analysis showed that higher dosages can, in fact, lead to higher bacterial loads. This is because selection for drug resistance is mediated by the duplication of the genes, AcrAB-TolC, that encode the aforementioned efflux pump. As explained in detail below, our work highlights the idea that Darwinian selection on additional copies of AcrAB-TolC is a non-linear function of antibiotic dose and that the observed transition from monotone to non-monotone dose-response is a consequence of AcrAB-TolC being strongly selected at very specific dosages. We term this phenomenon an ‘evolutionary hotspot’. Next, we extended the above experimental system to solid media to study how selection on resistance mediated by AcrAB-TolC leads to a ‘spatio-genomic patterning’ effect that we call a ‘bullseye’. Using a bespoke culture device developed as part of this PhD, we show that spatial selection on resistance also depends non-linearly on the distance of the cell from an antibiotic source, and that the non-linearity can be multi-modal as a function of distance, and therefore also of antibiotic dose. This result also contradicts the aforementioned principle that higher antibiotic dosages necessarily lead to fewer bacterial cells. Following on from this, we then studied the ability of microbial competitors for resources to modulate the antibiotic sensitivity of a particular strain of E. coli, namely Tets , using a range of multi-species experiments. We measured the sensitivity to antibiotics of Tets both with, and without, one bacterial or fungal competitor. When that competitor was equally sensitive to the antibiotic, we observed that Tets was less sensitive to it, in part due to an ‘antibiotic sinking’ effect carried out by the competitor strain. However, when the competitor was not sensitive to the antibiotic, Tets was, accordingly, more sensitive than in the absence of competition. In this latter case, the competitor seemed to reduce the growth of Tets by carbon theft as part of a phenomenon known as ‘competitive suppression’. Moreover, this ecological effect is one that synergises with the action of the antibiotic. Finally, we turned to a study of an ecological trade-off motivated by ribosome-binding antibiotics. So, by manipulating the content of ribosomal RNA in the E. coli cell, a large and essential molecule that is bound by antibiotics such as tetracycline or erythromycin, we could subsequently manipulate what is known as a metabolic trade-off between growth rate and growth yield. The latter is the number of cells produced per molecule of carbon found in the extracellular environment of the bacterial population. Using glucose as carbon source we therefore constructed an empirical fitness landscape that shows how the optimum number of ribosomal rRNA operons depends on extracellular glucose concentration. Whilst this study does not relate directly to the presence of an antibiotic, it does show that by altering the number of operons in a manner that is known to affect antibiotic susceptibility, we can also mediate important growth parameters like cell yield, aka efficiency, and growth rate.
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Simmer, Reid A. „Source determination and predictive model development for Escherichia coli concentrations at F.W. Kent Park Lake, Oxford, Iowa“. Thesis, University of Iowa, 2016. https://ir.uiowa.edu/etd/2142.
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Fecal contamination of Iowa recreational water bodies poses a threat to water quality as well as human health. Concern regarding the health effects of waterborne pathogens resulted in 149 beach advisories across 39 state-owned beaches during the 2015 beach season alone. While the presence of pollution is often clear, its cause and source may be difficult to identify. Furthermore, the current practice in Iowa of sampling once per week leads to high uncertainty and inadequately protects swimmers from exposure.
The objective of this study was to determine the influential environmental factors and sources causing spikes in fecal contamination at F.W. Kent Park Lake in Oxford, IA, and to develop a predictive model of beach E. coli concentrations. Water samples were collected at the swimming beach as well as throughout the watershed from May to October, 2015. All samples were analyzed for Escherichia Coli using the IDEXX Colilert enumeration method. Together with weekly data from 2012 through 2014, two predictive models of E. coli based upon influential environmental and water quality variables were developed using EPA Virtual Beach software. These models proved to be more accurate than the current method used to assess risks to swimmers that assumes bacterial concentrations remain constant between samples. In addition, through statistical analysis and modeling, this study found evidence that the main source of fecal contamination were wild geese that frequent the beach.
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Li, Zhuo 1982. „Deposition of model viruses on cellulose“. Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=116088.
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A bioactive paper is a paper that can detect, capture and deactivate water and airborne pathogens. In this project, we presented a model "bioactive paper" made by attaching T4 bacteriophages to a cellulose substrate. T4 bacteriophages can be genetically engineered to possess copies of cellulose-binding modules (CBM) on their capsids. This allows them to bind specifically onto cellulose surfaces. Our model surface is a thin film of regenerated cellulose made by spin coating a glass or quartz substrate with a cellulose triacetate and subsequently hydrolyzing the surface back to cellulose. We successfully demonstrated the attachment of the CBM-T4 bacteriophages onto cellulose substrates by the phage viability test. The deposition kinetics were measured using an impinging jet apparatus combined with an evanescent wave light scattering (EWLS) system. We first tested the apparatus by using amidine latex particles deposited on the cellulose at different flow rates and found them to be in a good agreement with the constant potential double-layer model. The adhesion experiments were also performed in an impinging jet apparatus in which the CBM-T4 bacteriophages and the unassembled protein complexes from a suspension of 4.08 x 10 8 PFU/mL were allowed to diffuse to the cellulose surface, The competitive diffusion kinetics were again studied by the EWLS technique. For CBM-T4, the blocking time was found to be around 58 minutes and the maximum surface number density of phages was 5.9 x 1010 per m 2.Key phrases: bioactive paper, cellulose film, cellulose binding module, bacteriophage T4, evanescent wave light scattering, unassembled protein complex, diffusion kinetics
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Faraj, Tabrizi Pouriya [Verfasser], Tim [Akademischer Betreuer] Maisch und Uwe [Akademischer Betreuer] Ritter. „Susceptibility of sodA- and sodB-deficient Escherichia coli mutant towards antimicrobial photodynamic inactivation via the type I-mechanism of action / Pouriya Faraj Tabrizi ; Tim Maisch, Uwe Ritter“. Regensburg : Universitätsbibliothek Regensburg, 2019. http://d-nb.info/1188887009/34.
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Lavrrar, Jennifer L. „The role of regulatory proteins at the FEPDGC-ENTS promoter region in escherichia coli : a new model for the fur-DNA interaction /“. free to MU campus, others may purchase free online, 2002. http://wwwlib.umi.com/cr/mo/preview?3074419.
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Angardi, Vahideh. „Influence Of Oxygen Transfer On Benzaldehyde Lyase Production By Recombinant Escherichia Coli Bl21(de3) Plyss“. Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608779/index.pdf.
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In this study, the effects of oxygen transfer conditions on the synthesis of the enzyme benzaldehyde lyase as intracellular in recombinant E. coli BL21 (DE3) pLysS was investigated sistematically and a comprehensive model was developed to determine benzaldehyde lyase activity. For this purpose, the research program was carried out in mainly two parts. In the first part of study, the effects of oxygen transfer together with the mass transfer coefficient (KLa), enhancement factor E (=KLa/KLao), volumetric oxygen transfer rate, volumetric and specific oxygen uptake rates, mass transfer and biochemical reaction resistancesmoreover, the variation in product and by-product distribution, specific substrate uptake rates, yield and maintenance coefficient were investigated in the pilot scale batch bioreactor at QO/VR = 0.5 vvm and agitation rates of N= 250, 500, 625, and 750 min-1, and dissolved oxygen levels DO= 20%, 40% conditions, while medium components were CGlucose= 8.0 kg m-3, C(NH4)2HPO4= 5.0 kg m-3 and salt solution at controlled pHc=7.2. The highest cell concentration and benzaldehyde lyase activity were obtained at DO=40% condition as 3.0 kg m-3 and A=1095 Ucm-3, respectively. v Then a mathematical model was proposed to estimate benzaldehyde lyase activity as function of time, agitation rate, cell concentration, dissolved oxygen concentration, and by-product concentration with reasonable accuracy.