No description available.

Hannover, Universiẗat, Diss., 2003.

Master of Science / Department of Diagnostic Medicine/Pathobiology / Sanjeev Narayanan / The use of antimicrobials in animal feed has come under increasing scrutiny from the public and regulatory agencies. Direct-fed microbials (DFM) are considered valuable alternatives to antimicrobials in food animal nutrition. DFM are products containing live (viable microorganisms). Studies in Europe have reported antimicrobial resistance (AMR) in organisms used in DFM. This is of serious concern because of the potential for transferring resistance to pathogenic bacteria in the gut. The aim of the present study is to characterize phenotypic and genotypic AMR profiles for 20 different antimicrobials in bacterial strains isolated from 10 commercially available DFM used in. Two antimicrobial susceptibility testing methods, disc diffusion and broth micro-dilution based assay were performed. Enterococcus faecium isolates showed resistance towards metronidazole (n=9/9) with a MIC of > 32 μg/mL, erythromycin (n=5/9) with a MIC of ≥ 8 μg/mL, ciprofloxacin (n=2/9) with a MIC ≥ 4 μg/mL, ceftriaxone (n=6/9) with a MIC ≥ 0.25 μg/mL, rifampin (n=8/9) with a MIC of > 4 μg/mL, trimethoprim/sulfamethoxazole (n=4/9) with a MIC ≥ 1 μg/mL and clindamycin (n=5/9) with a MIC of > 0.5 μg/mL. A Propionibacterium freudenreichii isolate showed resistance towards kanamycin with a MIC of > 64 μg/mL. The same strain also had a MIC of 16 μg/mL for levofloxacin. Two Lactobacillus acidophilus were resistant to vancomycin (n=2/6) with a MIC ≥ 32 μg/mL. All the Lactobacillus species including L. acidophilus (n=6), L. casei (n=4) and L. plantarum (n=2) were resistant to metronidazole, MIC > 32 μg/mL. Two strains of Bacillus subtilis showed resistance to clindamycin, with an MIC of 4 μg/mL and erythromycin with an MIC of > 8 μg/mL, and one strain had no zone of inhibition for metronidazole (MIC > 32 μg/mL). Microarray analysis revealed resistance genes in E. faecium strains of 3 different DFM, including aminoglycoside resistance genes, ant(4’)-Ia, erythromycin resistance genes, ere(A2) and ermB, tetracycline resistance genes, tet39, tet31, tetK and tetC, and beta-lactam resistance gene, pbp5. Conjugation with filter mating showed erythromycin resistance gene transfer, msrC gene, from donor strains to a recipient strain (E. faecium 45-24). These studies show that AMR is prevalent among bacterial strains used as DFM in the cattle industry in the U.S., justifying further characterization, detection and observation of transferable antibiotic resistance between the same genus. .

Consolidated bioprocessing is a one-step process that allows the direct microbial conversion of cellulosic substrates to ethanol and hydrogen. The fermentation was initially performed in batch cultures, in a pH and temperature controlled reactor using Clostridium thermocellum ATCC 27405. With an objective of increasing the production of ethanol and hydrogen, various types of fed-batch fermentations were investigated: variable volume (VV) fed-batch, fixed volume (FV) fed-batch, and semi-continuous fermentation. Semi-continuous processes were carried out at low (10-15 g/L) and high (20-25 g/L) cellulose concentrations. The maximum ethanol production obtained in batch, VV, FV, semi-continuous with low concentrations and high concentrations were 554 mmol, 336 mmol, 477 mmol, 695 mmol and 741 mmol respectively. In the same order, the total hydrogen production was 288 mmol, 364 mmol, 231 mmol, 434 mmol, and 387 mmol. Overall, the semi-continuous fermentation showed more promise in terms of large-scale deployment compared to batch, VV, and FV fed-batch. / October 2015

No description available.

Master of Science / Department of Diagnostic Medicine/Pathobiology / Sanjeev K. Narayanan / The use of antimicrobials in animal feed has come under increasing scrutiny from the public and regulatory agencies. Direct-fed microbials (DFM) are considered valuable alternatives to antimicrobials in food animal nutrition. DFM are products containing live (viable microorganisms). Studies in Europe have reported antimicrobial resistance (AMR) in organisms used in DFM. This is of serious concern because of the potential for transferring resistance to pathogenic bacteria in the gut. The aim of the present study is to characterize phenotypic and genotypic AMR profiles for 20 different antimicrobials in bacterial strains isolated from 10 commercially available DFM used in. Two antimicrobial susceptibility testing methods, disc diffusion and broth micro-dilution based assay were performed. Enterococcus faecium isolates showed resistance towards metronidazole (n=9/9) with a MIC of > 32 µg/mL, erythromycin (n=5/9) with a MIC of ≥ 8 µg/mL, ciprofloxacin (n=2/9) with a MIC ≥ 4 μg/mL, ceftriaxone (n=6/9) with a MIC ≥ 0.25 μg/mL, rifampin (n=8/9) with a MIC of > 4 µg/mL, trimethoprim/sulfamethoxazole (n=4/9) with a MIC ≥ 1 μg/mL and clindamycin (n=5/9) with a MIC of > 0.5 µg/mL. A Propionibacterium freudenreichii isolate showed resistance towards kanamycin with a MIC of > 64 µg/mL. The same strain also had a MIC of 16 µg/mL for levofloxacin. Two Lactobacillus acidophilus were resistant to vancomycin (n=2/6) with a MIC ≥ 32 μg/mL. All the Lactobacillus species including L. acidophilus (n=6), L. casei (n=4) and L. plantarum (n=2) were resistant to metronidazole, MIC > 32 µg/mL. Two strains of Bacillus subtilis showed resistance to clindamycin, with an MIC of 4 µg/mL and erythromycin with an MIC of > 8 µg/mL, and one strain had no zone of inhibition for metronidazole (MIC > 32 µg/mL). Microarray analysis revealed resistance genes in E. faecium strains of 3 different DFM, including aminoglycoside resistance genes, ant(4’)-Ia, erythromycin resistance genes, ere(A2) and ermB, tetracycline resistance genes, tet39, tet31, tetK and tetC, and beta-lactam resistance gene, pbp5. Conjugation with filter mating showed erythromycin resistance gene transfer, msrC gene, from donor strains to a recipient strain (E. faecium 45-24). These studies show that AMR is prevalent among bacterial strains used as DFM in the cattle industry in the U.S., justifying further characterization, detection and observation of transferable antibiotic resistance between the same genus.

Monitoring the limiting reactant concentration is a key question to maximize the productivity and to guarantee the safety of exothermic fed-batch processes. However in most applications, the concentration cannot be measured in real-time since suitable devices do not exist or are too expensive; the concentrations are then measured by off-line analyses. In this context monitoring the concentrations via software sensors, or state observer based estimators, is an attractive option. The presence of model uncertainties is a major limitation when applying state observers to real processes. More precisely, in fed-batch exothermic reactors the bad knowledge of both the reaction kinetics and the heat transfer may prevent the use of classical observers. In this study, we propose two different approaches to estimate the concentration of the limiting reactant in a class of single phase exothermic fed-batch reactors with uncertain kinetics and heat transfer. The first approach is based on a finite time converging observer that provides an estimate for the reaction rate via the reactor energy balance equation. The concentration is then computed from the reaction rate estimate via a material balance equation. The main contribution of this approach is the use of a finite time observer to limit the reconstruction error by guaranteeing a small convergence time interval for the reaction rate estimate. The second approach is based on an interval observer that provides two bounds for the concentration by considering uncertainties related to both the heat transfer and the reaction kinetics. The final estimate is then computed as the mean of the bounds. A systematic tuning procedure has been developed for each of both estimation techniques. Both estimators have then been tested and validated with real data coming from the production of different kinds of resins carried out in 10 tons reactors.

Master of Science / Department of Agricultural Economics / Glynn T. Tonsor / The past several years has marked one of the most heightened periods of fed cattle basis volatility since the installment of live cattle futures contracts. Understanding basis, the difference between local cash price and the futures contract price, is imperative when making marketing and procurement decisions. In the face of increased volatility, the ability to produce accurate basis expectations is no simple task. The purpose of these analyses was to develop econometric models to determine the greatest influencers of fed cattle basis, to test the presence of structural changes in the determinants of fed cattle basis, and to compare out-of-sample forecasting performance. This study analyzed in-sample econometric models using monthly data from January 2003 through September 2016, then compared the results of the competing models. Using the same time period, we then identified the presence of structural breaks in the data. Furthermore, this study analyzed the out-of-sample forecasting performance for January 2012 through September 2016. The out-of-sample results were then compared to in-sample estimations and historical average basis models. The in-sample estimations indicated the important factors that influence fed cattle basis. The results indicate that there are multiple structural breaks present in the determinants of fed cattle basis examined during this study. We can robustly conclude that there was a market structural break present in the fourth quarter of 2013 and within the 2005-2006 time period. The results indicate that the out-of-sample regression estimations were outperformed by historical average models and did not improve our ability to accurately forecast basis. Overall, a 3 or 4 year historical average model should be preferred over econometric estimations when forecasting fed cattle basis.

Animal cell culture is widely used as a platform for the production of a variety of biopharmaceuticals. The development of an efficient and productive cell culture requires a deep understanding of intra-cellular mechanisms as well as extra-cellular conditions for optimal synthesis. Mathematical modeling can be an effective strategy to predict, control, and optimize cell performance under different culture conditions. This research presents the evaluation of Chinese hamster ovary (CHO) cell culture secreting recombinant anti-RhD monoclonal antibody (MAb) through different processing modes, namely batch, fed-batch and perfusion operations. The ultimate objective of this study was to establish a comprehensive dynamic model which may be used for model-based optimization of the cell culture for MAb production in both batch, fed-batch or perfusion systems. In analyzing process performance, the key potential cause of cell growth inhibition was attributed to lowering of pH in the culture possibly due to the accumulation of dissolved carbon dioxide. The most important finding in this regard was the significantly different observed maximum total viable cell density in two identical cultures differing in culture volume only (250mL and 500mL). However, the other byproduct metabolites such as lactate and ammonia and glucose depletion were also capable affecting growth adversely causing growth arrest, viability reduction, apoptosis initiation and progress. Employing the experimental results of nutrient consumption, metabolite and biomass production, a metabolic flux based methodology was developed for modeling the metabolism of a CHO cell line. The elimination of insignificant fluxes resulted in a simplified metabolic network which was the basis for modeling the significant extracellular metabolites. Using kinetic rate expressions for growing and non-growing subpopulations, a logistic model was first developed for cell growth and dynamic models were formulated to describe culture composition and monoclonal antibody (MAb) secretion. The viable cell population was assumed to consist of normal growing, normal non-growing and apoptotic cell subpopulations. The rate of apoptotic cell formation was assumed to have a second order dependence on the normal cell concentration. The proposed mathematical model for metabolites included distinct terms that reflected the metabolic rates of growing and non-growing cell populations. The model was validated for a range of glutamine and glucose concentrations. Good agreement was obtained between model predictions and experimental data. In subsequent steps the attempt was to correlate the growth kinetics to significant variables of the culture. The regulatory effects identified through each culture condition were combined for a rational design of a dynamic model constructed for the viable cell subpopulation. A Tessier-based model was applied for defining the fraction of growing cells as a function of a growth inhibitor, presumably dissolved carbon dioxide. Although only few variables appeared in the biomass model, all equations were solved simultaneously. The parameters were estimated using the Metropolis-Hastings algorithm and the fmincon function in MATLAB. The final model adequately predicted the effect of significant variables on the metabolic behavior of CHO cells in batch, fed-batch and perfusion systems.

The thesis describes an optimal selective harmonic elimination strategy suitable for singlephase AC-DC converter-fed traction drives. The objective is to eliminate low-order supply current harmonics, including those injected into the supply due to load-side current ripple. Other advantages that the switching strategy has to offer over phase-control include improved supply power factor, reduced VA consumption for a given demand speed and load, reduced torque and speed ripple and smaller armature circuit smoothing inductance. The effect of field current boost on the dynamic response of the drive is also described. It is shown that field boost helps to reduce the speed rise-time by increasing the electromagnetic torque available during acceleration periods. Closed-loop control of a 4-quadrant DC drive is described and a comparison made between the performance of PID-control and pseudo-derivative feedback control. It is shown that pseudo-derivative feedback control has several advantages to offer, amongst which are ease of tuning of the controller gains and a superior performance following load torque disturbances. A laboratory size drive system was designed and built, and used to validate simulation predictions for both the switching strategy and pseudo-derivative feedback control. A microcontroller based hardware implementation of both the switching strategy and a digital pseudo-derivative feedback controller was adopted, with the switching strategy being implemented using an off-line approach of precalculating the switching angles and storing these in look-up tables. The armature voltage controller comprises a dual-converter employing IGBTs as switching devices. The use of IGBTs allows higher switching frequencies at significant power levels than would be possible if GTOs were used. It also simplifies the gate drive circuit design and minimises the need to use snubber circuits.