There are approximately 10^14 bacteria belonging to nearly 1000 different species in the human gastrointestinal (GI) tract that co-exist with host cells. Within the GI tract, signaling molecules secreted by both eukaryotic and prokaryotic cells are abundant. Recent studies have shown that both bacteria and human cells recognize and respond to the signals from each other, presumably to gain a competitive advantage. The cross-recognition of signals is known as Inter-kingdom (IK) signaling and this phenomenon is considered to be important in the onset of infections in the GI tract. Of the eukaryotic signaling molecules present in the GI tract, the neuroendocrine hormone norepinephrine (NE) is considered to be important in the context of infections as NE is produced at very high concentration in the intestine under post traumatic stress, is known to increase bacterial virulence and infection, and has also been shown to be a potent chemoattractant for GI tract pathogens such as enterohemorrhagic E. coli (EHEC). The focus of this study is on elucidating the mechanisms underlying the recognition and chemotaxis of bacteria towards NE. While chemotaxis has been typically investigated in the context of bacteria moving towards a metabolizable source (e.g., amino acids), chemotaxis is potentially important in the onset of infections in the human GI tract. In this study we use a microfluidic plug assay to investigate the receptor and mechanism utilized by a model bacterium Escherichia coli in its chemotactic response to NE. A series mutant of E. coli RP437 strains of knockouts for four MCP-encoding genes was used in this study. The results from the microfluidic plug assay were then confirmed quantitatively by capillary assay. We have shown that Tsr receptor is necessary for chemotaxis of NE for E. coli RP437, and attraction of E. coli towards NE may require an additional receptor. Results from the priming experiments suggest that exposure to NE may result in the de novo expression of co-receptor(s) that are crucial to chemotaxis towards NE. The requirement for high cell density also suggests the possibility that NE per se may not be an attractant for E. coli, but could be a precursor that is modified into a chemoattractant by cells. These results are expected to further our understanding of bacterial chemotaxis and its role in bacterial colonization and infection of the human GI tract.

Despite their beneficial effects, concerns have been raised about the role of antimicrobial growth promoters (AGP) in the emergence of antibiotic resistant bacteria. This study evaluated the effects of approved AGP on the emergence of antibiotic resistance in commensal E. coli and foodborne pathogen Salmonella. A survey of antibiotic resistance levels in commercial broiler chicken farms in the Fraser Valley (B.C.) and an experimental feeding trial were conducted from May 2004 to February 2005 and May to November 2005, respectively. The latter examined the effects of ten AGP formulations (bambermycin, penicillin, salinomycin, bacitracin, combination of salinomycin and bacitracin, chlortetracycline, virginiamycin 11ppm, virginiamycin 22ppm, monensin and narasin) on bird performance as well. Multiple antibiotic resistant commensal E. coli and Salmonella carrying virulence genes were found at commercial broiler chicken farms and therefore may serve as reservoirs for these genes. There was no significant difference between feed formulations on the phenotypic or genotypic characteristics of the isolates, except for tetracycline resistance gene tet(B). In the experimental feeding trial, broiler chickens were fed a diet including or excluding AGP. Birds were sampled prior to and weekly during feeding of the control and the AGPP containing diets. Although not detected on day 0, E. coli increased after day 7 to more than 9.9 log10 CFU/g in ceca. Multi-drug resistant E. coli were isolated from birds fed the ten AGP containing diets as well as the control diet. Except for penicillin, none of the AGP containing diets significantly improved bird performance compared to the control diet (P>0.05). Good management practices can significantly improve broiler chickens performance and decrease the mortality rate.

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.

Two leaves of amendments in pocket on front end paper. / Bibliography: leaves 177-185. / xix, 194 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Describes selective and nonselective procedures to extract recombinant protein from the cytoplasm of Escherichia coli. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1997

Reprints to two articles published by the author held in pocket in back of publication / x, 158, xxvi leaves : ill. ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Microbiology, 1974

Typescript (photocopy) / 146 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.) Dept. of Microbiology, University of Adelaide, 1982

Journal reprint in end pocket / vi, 229 leaves : photos., graphs, tables ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Microbiology, 1979

Diss. (sammanfattning) Umeå : Univ., 2007. / Härtill 5 uppsatser.

Thesis (Ph.D.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references (ℓ. 105-133)

Thesis (Ph. D.)--University of Adelaide, 1985. / Includes bibliographical references (leaves 267-287).