Thèse (M.Sc.) -- Université Laval, 1998. / Bibliogr.: f. [119]-173. Publié aussi en version électronique.

Eight foodborne pathogenic and spoilage Gram-positive bacteria were evaluated for their spontaneous resistance frequencies to the peptide antimicrobial nisin. In brain heart infusion (BHI) medium, nisin resistance frequencies were in the range of l06 to l08 when exposed to nisin at concentrations 2 to 4 times the minimal inhibitory concentrations. A stable nisin resistant mutant of Listeria monocytogenes Scott A was obtained by increasing stepwise exposure to nisin and subsequently characterized. Phospholipid content, fatty acid composition, phase transition temperature (Tc), and specific growth rates of the resistant mutant and parent were determined. The Tc of the resistant mutant (44.4°C) in comparison of the parent (37.4°C) indicated that significant changes occurred in the lipid composition of the mutant. Gas chromatographic analysis of fatty acids of mutant and parent revealed significant differences (P<0.05) in the proportional ratios of fatty acids; 14:0, 15:0 iso, 15:0 anteiso and 17:0 iso. cells and the concentration of nisin required for reaching a 50% maximum killing rate was five times that of sensitive cells. The bactericidal activity of nisin was more effective at 37°C than 4°C for both resistant and sensitive cells, but there was always higher survival of resistant cell than sensitive cells for both temperatures. Nisin degradation and plasmid involvement were demonstrated to not be the responsible resistance mechanism to nisin in L. monocytogenes. No cross-resistance was observed to therapeutically important antibiotics (rifampicin, chloramphenicol, vancomycin, erythromycin) and to metabolic inhibitors (CCCp, DCCD) by the nisin-resistant mutant. / Graduation date: 1993

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Food Science." Includes bibliographical references (p. 116-130).

No description available.

Listeria monocytogenes is a Gram-positive bacterium that is found ubiquitously throughout nature and is the etiologic agent of listeriosis. The majority of human listeriosis is foodborne, resulting from the consumption of unpasteurized and ready-to-eat foods that are contaminated during food processing. During the 2008 nationwide outbreak, the Gilmour laboratory performed the first real-time application of high-throughput whole-genome sequencing (WGS) of outbreak strains. Within this genomic data, the 77 kb plasmid, pLM5578, was newly identified in a clinical isolate, and additional Listeria plasmids (the 80 kb pLM5026 and the 60 kb pLM0813) were subsequently identified after WGS was completed on an expanded panel of outbreak isolates. Little was known regarding how plasmids contribute to persistence and virulence of L. monocytogenes, and to investigate these potential relationships, a panel of 147 L. monocytogenes food, environmental, and clinical isolates from Canadian public health events from the last three decades was selected for further study of the plasmids they might contain. Strain carriage of plasmids was determined using conventional PCR targeting known plasmid gene targets. Bioinformatic analyses were then used to predict the functions of individual genes encoded by each sequenced plasmid. These analyses were then used to direct experiments investigating the functions and associated phenotypes conferred by plasmid carriage. Phenotypic analyses included antimicrobial susceptibility testing, heavy metal resistance, and biofilm formation assays. Finally, WGS analyses was performed on isolates with plasmid screening patterns that indicated carriage of potential novel plasmids. Screening revealed that 75 of 147 isolates were positive for the presence of a plasmid, for which WGS analysis identified 24 unique newly identified L. monocytogenes plasmids. Phenotypically, 15 of these plasmids were found to contribute to a decreased susceptibility to the heavy metal cadmium, whereas 4 conferred resistance to the sanitizer benzalkonium chloride. Plasmid carriage was also found to affect biofilm formation. Nine plasmids correlated with stronger biofilm formation phenotypes; whereas 5 plasmids were correlated with weaker biofilm formation phenotypes. No known virulence factors or antibiotic resistance determinants were present in the DNA sequences of these 24 newly identified plasmids. Numerous coding sequences predicted to assist with survival under environmental stress were identified, and it is hypothesized that these plasmids likely contributed to persistence of L. monocytogenes within food processing environments.

Thesis (DR. P.H.)--University of Michigan.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Jan. 15, 2009). PDF text: 197 p. : ill. (some col.) ; 1.61 Mb. UMI publication number: AAT 3315877. Includes bibliographical references. Also available in microfilm and microfiche formats.

Würzburg, Univ., Diss., 2008 / Zsfassung in engl. Sprache

Thesis (M.S.) in Microbiology--University of Maine, 2003. / Includes vita. Includes bibliographical references (leaves 36-40).

Thesis (DR. P.H.)--University of Michigan.