Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Includes bibliographical references. Issued in print and online. Available via ProQuest Digital Dissertations.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 77-86). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 77-86). Also available on the Internet.

Thesis (M.For.Sc.)--University of Western Australia, 2007.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 157-190).

Master of Science / Department of Diagnostic Medicine/Pathobiology / Daniel U. Thomson / Escherichia coli O157:H7 is a human food-borne pathogen and cattle feces are a major source of contamination. Immunization against E. coli O157 may be a practical pre-harvest intervention strategy. A siderophore receptor/porin proteins (SRP) based vaccine has been developed to decrease the prevalence of E. coli O157 in cattle. Two studies were conducted to determine the efficacy of the SRP vaccine. In the first study, thirty calves were randomly assigned to one of two groups: control or SRP vaccine. Two weeks after the second vaccination, calves were orally inoculated with nalidixic acid-resistant (Nal[superscriptR]) E. coli O157. Fecal samples were collected for five weeks. Calves were necropsied on day 35 to collect gut contents and tissue swabs to determine Nal[superscriptR] E. coli O157:H7. The number of calves that were culture positive for E. coli O157 were lower (P= 0.07) in vaccinated group compared to the control. In the second study, cattle in two feedlots were randomized to SRP vaccine or control. Cattle were vaccinated on days 0 and 21. Rectal fecal samples were collected on day 0, and pen floor samples were collected on days 21, 35, and 70. Rectal fecal samples, RAMS, and hide swab samples were collected on d 85. Cattle were weighed on days 0, 21, and 85. Vaccination significantly reduced (P = 0.04) fecal E. coli O157 prevalence. There was also a decrease (P < 0.05) in E. coli O157 prevalence on hides and in fecal samples on day 85 in vaccinated cattle compared to the control.

Rapid detection of foodborne pathogen is one of the most urgent problems in the world, because foodborne pathogen could cause serious illness, such as nausea, vomiting and diarrhea. We have developed a sensitive microfluidic system based on dendrimers and aptamers for rapid detection of Escherichia coli O157:H7 at very low cells concentration. Dendrimers, with high level of functional groups and homogeneous spherical shape, are prefect nanoscale polymers used as a template material by increasing sensitivity and specificity of analytes detection in microfluidics. In this work, we develop a sensitive microfluidic system based on dendrimers and aptamers for detecting Escherichia coli O157:H7 at very low cell concentrations. Carboxyl functionalized G7-polyamidoamine (PAMAM-COOH) dendrimers are immobilized on (3-aminopropyl)-trimethoxysilane (APTMS) pretreated microfluidic channels. The aptamers are subsequently conjugated on the immobilized dendrimes through chemicals. The sensitivity and specificity are validated by injecting fluorescein isothiocyanate (FITC) labelled Escherichia coli O157:H7 at various cells concentration into the resulting microchannels, indicating that the detectable cells concentration can be reached as low as 100 (cells/ml) and the detection time is 10 hours. To further exploit and improve the work efficiency our microfluidic device, the microfluidic channel is designed into a staggered herringbone microchannel (SHM) to create the chaotic dynamics inside the microfluidic device, and the SHM is then simulated by a COMSOL software showing that the staggered herringbone structures can improve chaotic dynamics of designed microchannel and will enhance the probability of particles to attach on the surface of microdevice. All the results show that our approach has the potential to develop the field of rapid and accurate detection on foodborne pathogens.

The house fly, Musca domestica can transmit human pathogens including Escherichia coli O157:H7 through regurgitation of ingested bacteria from the crop which is a foregut organ of house fly and stores the excess ingested nutrients. Interactions between the ingested bacteria and the crop have a direct influence on bacteria persistence, survival and ultimately fly vector competence. In this research, in situ crop vessel assay was developed to investigate bacterial growth within fly crops up to 48 hours post-ingestion. Flies were fasted for 12 h prior to feeding E. coli O157:H7 pEGFP and then fed bacteria with red food color which was added to confirm that flies had consumed the bacteria. After feeding, flies with red abdomens were aseptically dissected and crops were removed and maintained in sterile phosphate buffered saline in microtiter plates held at 32˚C. For each time point (0, 24 and 48 hours post-ingestion), five crops were homogenized individually using a tissue grinder and bacterial levels (CFU/crop) were monitored using plate counts. Confocal microscopy of intact crops was used to monitor biofilm development. There was no statistical difference in cell numbers (CFU/crop) over the 48 h incubation period. Microscopy showed that upon prolonged incubation, GFP-expressing E. coli within the crop produced biofilms. This method showed greater reproducibility in studying crop bacteria level than using a live fly feeding study. But this system was not recommended to study the interaction between bacteria and the crop of housefly.

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