A model of growth and plasmid transfer between strains of Escherichia coli and Salmonella typhimurium was developed with reference to the literature. This was the organising principle for the collection of a complete set of in vitro life history parameters of one S. typhimurium and one E. coli strain. In the course of estimating these parameters two results of note were obtained. Fits of the Lotka-Volterra competition model were obtained for data on S. typhimuiurm growing in competition with E. coli. The first noteworthy discovery was the failure of this model to account for several characteristics of growth of these strains under competition. The growth rates of plasmid-bearing and plasmid-free strains were obtained. The second main result came from examination of the results of the growth rate data, which revealed that the cost to S. typhimuiurm 576 of bearing the resistance plasmid was low (4%). The model was also used to simulate the effect of antibiotic dose on the density of the donor, recipient and transconjugant populations over time. These simulations predicted that there would be a convex relationship between antibiotic dose and transconjugant density (i.e. that the density would first rise, then fall, with increasing dose). Following from this result, laboratory experiments and in vivo experiments in chickens were directed towards obtaining information on the relationship between these two variables. This convex relationship was not demonstrated within a single experiment, although some experimental environments produced an increase in transconjugant density with dose, and others, a decrease. Few transconjugants were formed in vivo. In order to investigate the low cost of resistance and low rate of in vivo transconjugant production, cost of resistance and plasmid transfer rate of this plasmid in several strain combinations of E. coli and S. typhimuiurm was evaluated.

The global threat from antibiotic resistant organisms and the effect on human and animal health is now well acknowledged. One measure to control the emergence and dissemination of antibiotic resistant organisms is to monitor bacterial populations and examine the epidemiology of antibiotic resistance genes in naturally occurring bacteria. This study examines antibiotic resistant bacteria of human and animal origin and compares resistance gene transfer in the intestinal tract of animal models to that which occurs in vitro. / The study provides information about tetracycline resistance as it occurs in wild-type bacteria within the environment of the normal flora of an animal. The transfer of tetracycline resistance genes in vitro between E. coli isolates from different origins was found to be occurring at lower levels than that which occurred in vitro. The co-transfer of unselected spectinomycin, streptomycin and sulfadiazine resistance in animal models was also demonstrated. / The study has provided important information regarding the nature and epidemiology of antibiotic resistance in naturally occurring strains of E. coli and enterococci from Australia. This should form part of a larger study, which monitors commensal bacteria and collects data regarding antibiotic resistance in natural populations of bacteria. This evidence can then be used to reduce the levels of antibiotic resistance in the environment and reduce the risk to human and animal health. / Thesis (PhD)--University of South Australia, 2006.

Thesis (M. Phil.)--University of Hong Kong, 2007. / Also available in print.

Thesis (Ph.D.)--Murdoch University, 2004. / Thesis submitted to the Division of Health Sciences. Bibliography: leaves 214-249.

Thesis (MHSc--Health Science) -- Auckland University of Technology, 2004. / Also held in print (182 leaves, ill., 30 cm.) in Akoranga Theses Collection. (T 362.110993 JOW)

Thesis (Ph.D.)--Baylor University, 2008. / Includes bibliographical references (p. 130-146).

Thesis (M.S.)--University of Michigan, 1976.

Thesis (M.S.)--University of Alabama at Birmingham, 2008. / Description based on contents viewed May 30, 2008; title from title screen. Includes bibliographical references (p. 62-66).

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Additional advisors: Asim K. Bej, Susan K. Hollingshead, Daniel D. Jones, Stephen A. Watts. Description based on contents viewed June 23, 2009; title from PDF t.p. Includes bibliographical references.

Thesis (M.S.)--Michigan State University. Dept. of Microbiology & Molecular Genetics, 2008. / Title from PDF t.p. (viewed on July 29, 2009) Includes bibliographical references (p. 162-166). Also issued in print.