Files on accompanying CD-ROM: Appendix III Phages ST64T and ST64B sequences, are in rtf format. Bibliography: leaves 279-324. System requirements for accompanying CD-ROM: IBM or compatible ; Microsoft Word or compatible to read rtf files.

Corrigenda attached after the bibliography. / Bibliography: leaves 166-206. / 206 leaves [6] leaves of plates : ill. ; 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 Molecular Sciences, 2001

Files on accompanying CD-ROM: Appendix III Phages ST64T and ST64B sequences, are in rtf format. / Bibliography: leaves 279-324. / System requirements for accompanying CD-ROM: IBM or compatible ; Microsoft Word or compatible to read rtf files. / xii, 325, [8] leaves, [116] leaves of plates : ill. (some col.) ; 30 cm. + 1 CD-ROM (4 3/4 in.) / 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 Molecular Biosciences, 2002?

Thesis (M. Sc.)(Microbiology)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references (leaves 87-108). Available on the Internet via the World Wide Web.

The purpose of this work was to examine the effectiveness of several replacements for antibiotics in broiler chickens using bacterial challenge models. For this work, pathogen challenge models were developed using three model pathogens; two human pathogens (<i>Salmonella enteritidis</i> and <i>Campylobacter jejuni</i>), and one poultry pathogen (<i>Clostridium perfringens</i>). The first set of experiments involved the selection and use of 2 model probiotics; <i>Bifidobacterium animalis</i> and <i>Lactobacillus fermentum</i>. Oral administration of either probiotic did not significantly reduce (P < 0.05) the level of intestinal colonization by either <i>S. enteritidis</i> or <i>C. jejuni</i> in experimentally infected broiler chickens. The next set of experiments examined the effectiveness of orally administered, pathogen-specific antibodies obtained from hyperimmunizing laying hens in controlling bacterial infections with <i>S. enteritidis</i>, <i>C. jejuni</i> or <i>Clostridium perfringens</i> in broiler chickens. Regardless of the concentration, or mode of administration, anti-<i>S. enteritidis</i> hen-egg antibodies or anti-<i>C. jejuni</i> hen-egg antibodies were unable to significantly reduce (P < 0.05) the intestinal colonization by either pathogen in experimentally infected broiler chickens. Likewise, administration of anti-<i>C. perfringens</i> hen-egg antibodies did not reduce intestinal colonization by <i>C. perfringens</i>, and actually exacerbated the clinical outcome of this important poultry pathogen by significantly increasing (P < 0.05) intestinal lesions scores compared to negative control birds. Lastly, the effect of dietary protein source on intestinal <i>C. perfringens</i> populations was investigated. In broiler chickens experimentally infected with <i>C. perfringens</i> and fed diets which varied in the source of dietary protein, it was shown that birds fed fish meal, meat/bone meal, feather meal and potato protein concentrate had significantly higher intestinal <i>C. perfringens</i> counts than the birds fed corn gluten meal, soy or pea protein concentrates or the control diet (P < 0.05). Further, it was shown that the glycine content of the diets and ileal contents was significantly, positively correlated with <i>C. perfringens</i> numbers in ileum and cecum. It is concluded that although the intervention strategies employed in these studies show promise, diet composition clearly had the largest effect on intestinal bacterial populations. Further studies are required to examine both the impact that diet and these intervention strategies have on the factors which control intestinal colonization by pathogens on a case by case basis.

The bacterial protein H-NS acts to silence horizontally acquired genes. H-NS physically interacts via its N-terminus with two paralogous proteins, Hha and YdgT. Deletion of hha and ydgT results in derepression of a subset of H-NS repressed genes. I compared expression of hha/ydgT-dependent genes in Salmonella strains lacking hns and hha/ydgT/hns. Deletion of all three genes does not result in greater gene expression than deletion of hns alone, indicating that Hha and YdgT cannot act to repress genes in the absence of H-NS. Further, I used site-directed mutagenesis to generate H-NS proteins incapable of binding Hha. Complementing an hns deletion with an Hha-blind H-NS molecule, H-NS I11A, recapitulated the pattern of gene expression in the hha/ydgT strain. Indicating that elimination of the Hha-H-NS interaction is sufficient to result in derepression of hha/ydgT repressed genes. Hha and YdgT repress gene expression by acting through H-NS and cannot act independently of H-NS.

The bacterial protein H-NS acts to silence horizontally acquired genes. H-NS physically interacts via its N-terminus with two paralogous proteins, Hha and YdgT. Deletion of hha and ydgT results in derepression of a subset of H-NS repressed genes. I compared expression of hha/ydgT-dependent genes in Salmonella strains lacking hns and hha/ydgT/hns. Deletion of all three genes does not result in greater gene expression than deletion of hns alone, indicating that Hha and YdgT cannot act to repress genes in the absence of H-NS. Further, I used site-directed mutagenesis to generate H-NS proteins incapable of binding Hha. Complementing an hns deletion with an Hha-blind H-NS molecule, H-NS I11A, recapitulated the pattern of gene expression in the hha/ydgT strain. Indicating that elimination of the Hha-H-NS interaction is sufficient to result in derepression of hha/ydgT repressed genes. Hha and YdgT repress gene expression by acting through H-NS and cannot act independently of H-NS.

The purpose of this work was to examine the effectiveness of several replacements for antibiotics in broiler chickens using bacterial challenge models. For this work, pathogen challenge models were developed using three model pathogens; two human pathogens (<i>Salmonella enteritidis</i> and <i>Campylobacter jejuni</i>), and one poultry pathogen (<i>Clostridium perfringens</i>). The first set of experiments involved the selection and use of 2 model probiotics; <i>Bifidobacterium animalis</i> and <i>Lactobacillus fermentum</i>. Oral administration of either probiotic did not significantly reduce (P < 0.05) the level of intestinal colonization by either <i>S. enteritidis</i> or <i>C. jejuni</i> in experimentally infected broiler chickens. The next set of experiments examined the effectiveness of orally administered, pathogen-specific antibodies obtained from hyperimmunizing laying hens in controlling bacterial infections with <i>S. enteritidis</i>, <i>C. jejuni</i> or <i>Clostridium perfringens</i> in broiler chickens. Regardless of the concentration, or mode of administration, anti-<i>S. enteritidis</i> hen-egg antibodies or anti-<i>C. jejuni</i> hen-egg antibodies were unable to significantly reduce (P < 0.05) the intestinal colonization by either pathogen in experimentally infected broiler chickens. Likewise, administration of anti-<i>C. perfringens</i> hen-egg antibodies did not reduce intestinal colonization by <i>C. perfringens</i>, and actually exacerbated the clinical outcome of this important poultry pathogen by significantly increasing (P < 0.05) intestinal lesions scores compared to negative control birds. Lastly, the effect of dietary protein source on intestinal <i>C. perfringens</i> populations was investigated. In broiler chickens experimentally infected with <i>C. perfringens</i> and fed diets which varied in the source of dietary protein, it was shown that birds fed fish meal, meat/bone meal, feather meal and potato protein concentrate had significantly higher intestinal <i>C. perfringens</i> counts than the birds fed corn gluten meal, soy or pea protein concentrates or the control diet (P < 0.05). Further, it was shown that the glycine content of the diets and ileal contents was significantly, positively correlated with <i>C. perfringens</i> numbers in ileum and cecum. It is concluded that although the intervention strategies employed in these studies show promise, diet composition clearly had the largest effect on intestinal bacterial populations. Further studies are required to examine both the impact that diet and these intervention strategies have on the factors which control intestinal colonization by pathogens on a case by case basis.

In recent years, due to the increasing number of produce-related outbreaks, greater attention has been given to interventions that remove human pathogens on fresh produce. Survival of Salmonella Poona on the surface and stem scar portions of inoculated cantaloupe, effect of chlorine or lactic acid or ozone on the survival of bacteria, transfer of pathogen from the rind to the fresh-cut tissue during cutting and growth and survival of Salmonella Poona on the fresh-cut tissues during 15 days of refrigerated storage were investigated. Preliminary studies were conducted to confirm that the rifampicin-resistant strain used in the study was indistinguishable from the parent strain of Salmonella Poona. Growth curve, heat tolerance and lactic acid resistance studies were performed, all of which showed no differences in behavior between the organisms. Cantaloupes were immersed in an inoculum containing rifampicicn-resistant strain of Salmonella Poona (107 CFU/ml) for 3 min and then dried for 12 h. The inoculated melons were washed with chlorine (200 ppm) for 3 min or lactic acid (2%) for 2 min or ozone (30 ppm) for 5 min and fresh cut tissues were prepared by peeling the rind and cutting into pieces or cutting the melon and removing the rind. Results obtained indicate that the levels of Salmonella Poona recovered were higher when the sample was obtained from the scar portion than the surface. Surface treatment with tap water or chlorine did not reduce Salmonella Poona. However treatment with lactic acid or ozone reduced the levels by 2.5 and 2.3 log10 CFU/cm2 respectively on the surface. Fresh-cut tissue prepared from melons sanitized with lactic acid resulted in less transfer during cutting and reached below detectable limits after 9 days of refrigerated storage. Cutting melons after peeling the rind was found effective in reducing the transfer of Salmonella Poona into the tissue in comparison with cutting of melons and removing the rind later. Thus these data suggest that treatment with lactic acid and ozone may be effective in reducing Salmonella from the surface of the cantaloupe where as lactic acid was effective in reducing the transfer from the surface to the flesh.

There is increasing interest in developing methods to detect and identify Salmonella, to eliminate or reduce the risk of contamination of shell eggs, and to retain the economic advantages of induced molting without increasing the risk of Salmonella enteritidis infection. S. enteritidis and S. typhimurium are the most common serotypes among 2449 known serotypes of the Salmonella, and are the causes of most egg- related foodborne salmonellosis in humans in the U. S. These two species are also responsible for environmental contamination and the incidence of infections. Therefore, this study was conducted in three phases consisting of ten in vivo and in vitro experiments. This study investigated the effects of zinc on Salmonella growth and survivability in poultry environments, and its ability to induce a molt in single comb white leghorn hens. In part, the antibacterial properties of zinc may reduce environmental contamination in a poultry house by interrupting airborne routes. The first phase involved detecting airborne bacteria by aerosol sampling methods, and then screening any Salmonella mutant (s) that survived desiccation by transposon footprinting. The second phase examined, in vitro, the addition of zinc on the growth kinetics of Salmonella under aerobic or anaerobic conditions, the effects of combinating zinc and acidic conditions on the growth kinetics of Salmonella in vitro under aerobic or anaerobic conditions, and the effects of zinc amended feed on the survival of a dry inoculum of Salmonella. The third phase investigated the ability of zinc propionate, as an alternative salt form of zinc, to induce molt in laying hens, the influence of zinc acetate and zinc propionate on gastrointestinal tract fermentation, and susceptibility of laying hens to S. enteritidis during an induced molt, and the comparison of digestive microbial crop and cecal communities among molted hens fed by either zinc acetate or zinc propionate amended molting diets with hens undergoing feed withdrawal or full fed nonmolted hens using molecular-based denaturing gradient gel electrophoresis.