Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Filters

2006 - 200912010 - 20171

Settings

Subject: search.filters.subject.Escherichia coli O157:H7

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    WHOLE GENOME SEQUENCING ANALYSIS ON SHIGA TOXIN-PRODUCING ESCHERICHIA COLI O157:H7 FROM CATTLE FED WITH DIFFERENT DIETARY PROTEIN CONCENTRATIONS
    (2017) YANG, XUN; MENG, JIANGHONG; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Escherichia coli serotype O157:H7 was first recognized in 1982 as a human pathogen associated with outbreaks of bloody diarrhea in the United States and is now considered a major cause of foodborne infections because of its high hospitalization rate. Cattle is the major reservoir of E. coli O157:H7. Cattle harbor E. coli O157:H7 in the hindgut and shed the organisms in the feces, which serves as a source of contamination of food and water. It is hypothesized that dietary ingredients that reach the hindgut are likely to affect colonization and fecal shedding of STEC. Increased flow of dietary ingredients (starch, fiber, protein, and lipid) are likely to alter ecology of the hindgut, resulting in altered pH and fermentation products, which could have a positive or negative impact on E. coli O157:H7. The objectives of this study are to investigate E. coli O157:H7 populations in fecal shedding of cattle. The cattle in this study were fed with diets with different levels of ruminally-degradable and –undegradable protein. A total of 286 E. coli O157:H7 isolates were recovered from feces of 576 crossbred calves at the Clayton Livestock Research Center in Clayton, New Mexico. The organisms were sequenced using Illumina Miseq system. De novo assembly of raw reads was performed using SPAdes and SNPs analysis of the isolates was conducted using kSNP3. Virulence factor Database (VFDB), created by the MOH key laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, was used as a reference for BLAST. The results indicated that increased flow of undegradable protein may increase the shedding of E. coli O157. However, the effect of ractopamine was still unknown. Three clades were identified among the E. coli O157:H7 isolates, including clades 6, 7, and 8, most of which belong to clade 8 (205 of 286). 49588 SNPs were found according to kSNP3. 19043 SNPs were identified as core SNPs. The phylogenetic analysis showed that the E. coli O157 isolates which collected from neighboring Pens were more closely to each other.
  • Thumbnail Image
    Item
    Engineering-Based Probabilistic Risk Assessment for Food Safety with Application to Escherichia coli O157:H7 Contamination in Cheese
    (2006-04-26) Fretz, Kristin; Modarres, Mohammad; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A new methodology is introduced in which engineering-based tools and techniques are adapted to quantitative microbial risk assessment (QMRA) in order to offer a more systematic solution to food safety problems. By integrating available microbial data and adapted engineering techniques within the traditional QMRA framework, this new methodology addresses some of the deficiencies of traditional approaches. Through the use of a hierarchical structure, the system is decomposed into its most basic elements so that the interrelationships and interdependences of these basic elements are captured. This hierarchical structure also identifies variability throughout the process, resulting in a risk model in which multiple scenarios can be analyzed. In addition, the engineering approach adapts methods for characterizing and propagating uncertainties. Unlike the traditional approaches in food safety, the engineering-based methodology relies on mathematical models; the uncertainties about these models (both aleatory and epistemic), as well as the uncertainties about the model parameters, are formally quantified and properly considered. This separation and characterization of uncertainties results in a more powerful risk model, so that assessments can be made as to whether additional information or changes to the physical system will reduce the total uncertainty. Finally, this research characterizes the validity of the various dose-response models. Comparison of actual outbreak observations to model predictions lends credibility and assesses uncertainty of the developed dose-response models. Thus, the results of the risk model can be used both as an absolute assessment of risk and as a relative measurement of mitigation and control strategies. As a case study, the engineering-based methodology is applied to the problem of Escherichia coli O157:H7 contamination in cheese. While it has been assumed that pathogenic microorganisms in raw milk die during cheese-making, several studies on the survival of E. coli O157:H7 in cheese have demonstrated growth during cheese manufacturing. Furthermore, E. coli O157:H7 has been linked to several outbreaks involving cheese, thereby establishing the need to investigate this route of transmission. The successful application of the engineering-based approach to the problem of E. coli O157:H7 contamination in cheese suggests that this new methodology can be applied to other food safety problems.