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Shigatoxin-producing Escherichia coli (STEC) can cause infections in humans which can beserious and sometimes fatal. There is a great need for methods that are able to detect differentserogroups of STEC. In this project, conventional and real-time PCR assays for detection ofSTEC O104:H4 and O121, as recommended by the European Union Reference Laboratory(EU-RL) for STEC, were validated. The specificity, limit of detection, repeatability,efficiency and robustness were determined for three real-time PCR assays. The validationshowed that the real-time PCR reactions were specific and sensitive although some additionaltests are required.

Toxoplasma gondii is the causative agent of Toxoplasmosis in human and animals. T. gondii isolates are highly diverse. Hundreds of genotypes have been identified, but only three clonal lineages, namely Type I, II and III are prevalent worldwide. In mouse model, T. gondii strains can be divided into three groups based on their virulence, including the virulent (LD100=1), the intermediately virulent (LD50 = 103-104) and the non virulent (LD50 > 105). The clonal Type I, II and III T. gondii strains belong to these three groups, respectively. Epidemiologic studies suggest the difference of virulence in mice may relate to the severity of toxoplasmosis in human infection. Therefore, it is necessary to understand biological differences in genetically different T. gondii strains and their effect on the host responses. To date, the majority of data published on this aspect has been limited to in vitro assays. Here, we used in vivo assays to investigate host responses upon infection of distinct Toxoplasma strains. Our studies examined host response to infection of the three widespread clonal lineages of T. gondii using a mouse model. The following results were revealed: (i) increased tissue burden in mice is the indicator of virulence of T. gondii. Quantification of parasite burden in the spleen of mice showed significantly more parasites for Type I strain than that of Type II and III strains, with the latter two having comparable parasite burdens. Given that the Type II strains are more virulent than the Type III strains in mice; this result suggests that difference in host response is the result of specific parasite-host interaction, which is not simply due to the difference of parasite tissue load. (ii) gene expression in the host is strongly influenced by parasite genetic background. Transcriptional profiles of mice infected with the above three types of T. gondii strains showed that the overall gene expression patterns are similar between Type I and Type II infected mice and both stimulated stronger and more polarized change comparing to Type III strain. These results emphasize the importance of studying T. gondii pathogenesis in the host with the consideration of parasite genetic diversity. Such research could possibly aid in select appropriate regimes to treat toxoplasmosis caused by diverse T. gondii strains.

The organisms in this study were chosen due to their associations with foods and their potential as food borne pathogens. Food borne diseases are an import public health problem in most countries. Bacteria of the genera Campylobacter, Salmonella and Listeria can be transported by poultry and poultry products to humans. Gastroenteritis, typhoid fever, diarrhea, dysentery may originate from the infection. This study was undertaken to determine the incidence of pathogens in a poultry processing plant using polymerase chain reaction and conventional tests and to determine the formation and survival of biofilm cells of food pathogens in trisodium phosphate.

The entrainment of microbes from agricultural land into overland flow during rainfall events is recognised as an important source of pathogenic microbes to surface water bodies and yet this transport process is poorly understood. In this study, a method has been developed to separate bacteria into the forms in which they have been postulated to exist in overland flow. Then Escherichia coli was used as a model organism to investigate the transported state of bacteria eroded from cowpats and their subsequent transport in overland flow. Simulated rainfall experiments were used to generate runoff direct from cowpats. Concentrations of E. coli in the runoff direct from cowpats were found to be directly proportional to the concentration in the cowpat, regardless of the age of the cowpat. It was also observed that E. coli were predominantly eroded from cowpats as individual cells. The interactions between E. coli and soil particles in overland flow were then examined in a small laboratory scale model system and showed that E. coli attached to large (>45 [mu]m) soil particles were transported significantly less than unattached cells. However, in the runoff from the model system, E. coli were found to be attached mainly to clay particles that were similar in size to the bacterial cells. Furthermore, the transport of E. coli through the model system appeared to follow the transport of a conservative chemical tracer implying that (a) the cells were being transported as a solute with the bulk of the water flow, and (b) that E. coli attached to small clay particles were as mobile in the overland flow as unattached cells. These observations imply that E. coli predominantly interact with small clay particles that are also being carried along in the overland flow. The transport of E. coli at a larger scale was then investigated using 5-metre long, 1-metre wide buffer strips operated under saturation excess conditions. In buffer strips using intact soils and existing pasture cover, E. coli removal was very poor (26 % removal) at the low flow rate of 2 L min⁻� with no removal observed at the higher flow rates of 6 and 20 L min⁻�. E. coli removal rates were increased to 41 % removal at 2 L min⁻� by cultivating the soils, with the removal rate again decreasing with increasing flow rate. E. coli in the overland flow from the buffer strips did not form into large flocs or attach to large soil particles, but were transported in small neutrally buoyant particles that remain entrained in the overland flow. Under saturation excess runoff conditions, E. coli in overland flow were not effectively removed by buffer strips as the small particles are transported either over the soil surface or, through large pores in the soil. This Thesis has shown that E. coli is transported in overland flow in small particle sizes that are difficult to trap or remove from overland flow thereby explaining the high fluxes of faecal bacteria observed in overland flow from agricultural land.

Thesis (Ph.D.)--Murdoch University, 2002. / Thesis submitted to the Division of Veterinary and Biomedical Sciences. Bibliography: leaves 237-283.

Thesis (Ph.D.) in Food and Nutrition Sciences--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 150-176).

Thesis (Ph.D.)--McMaster University, 2006. / Supervisor: G.D. Wright. Includes bibliographical references.

Thesis (M.A.)--Humboldt State University, 2008. / Includes bibliographical references (leaves 98-104). Also available via Humboldt Digital Scholar.