[No abstract available] / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

[No abstract available] / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Aeromonas salmonicida sous-espèce salmonicida est un agent pathogène opportuniste responsable chaque année d’importantes pertes économiques pour les aquaculteurs de Salmonidés. Dans cette étude, plusieurs analyses ont été effectuées dans l’objectif de trouver une méthode pour distinguer entre différents isolats de cette bactérie au niveau génomique. Suite à l’alignement chromosomique des souches A449 et 01-B526, trente-deux altérations génomiques ont été répertoriées et elles peuvent être classées en cinq groupes : séquences d’insertions (13), séquences répétées en tandem (12), séquences insérées dans des gènes (5), site de polymorphisme multi-évènementiel (1) et îlot génomique (AsaGEI1a) (1). Des criblages PCR et des séquençages génomiques ont révélé l’existence de trois autres îlots génomiques (AsaGEI1b; AsaGEI2a; AsaGEI2b). Chaque AsaGEI est hautement spécifique à une région géographique. Les AsaGEI(1a; 2a) sont seulement observés en Amérique du Nord et les AsaGEI(1b; 2b) en Europe. Dans ces travaux, plusieurs marqueurs pouvant permettre d’identifier l’origine géographique des souches pathogènes ont été découverts. / Aeromonas salmonicida subsp. salmonicida is an opportunistic pathogen, which causes significant economic loss in salmonid aquaculture. In this work, analyses were conducted with the objective to find a way to distinguish between different isolates of the bacterium at the genomic level. Following the chromosomal alignment between A449 and 01-B526 strains, thirty-two genomic alterations were found and were classified in five groups: insertion sequences (13), tandem repeat sequences (12), CDS-modeling sequences (5), multi-event polymorphism site (1) and genomic island (AsaGEI1a) (1). PCR assays and genomic sequencing revealed the existence of four forms (AsaGEI(1a; 1b; 2a; 2b)) of the genomic island. Each GEI appeared to be strongly associated with a specific geographic region. AsaGEI(1a; 2a) were exclusively found in North American isolates and AsaGEI(1b; 2b) in those from Europe. In this study, several indicators useful to identify the geographical origin of pathogenic strains of this bacterium were discovered.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

The epidemiology of Aeromonas salmonicida subsp. salmonicida in the marine environment was investigated. Nutrient resuscitation and infectivity studies did not support a previous claim of dormancy in A. salmonicida and validated the use of colony-forming units (cfu) in survival studies. Survival of A. salmonicida in seawater was assessed and found to be of short duration «10 days). Survival of the bacterium in non-sterile sediment, obtained from beneath a salmon cage, appeared to be limited. The minimum infective dose of A. salmonicida to Atlantic salmon in short duration (1-3 days) bath exposure in sea water was 10' cfu ml-I. Prolonged exposure for three weeks resulted in infection with 102 cfu ml- I. Intragastric intubation of the bacterium established infection with doses >105 cfu. Shedding of A. salmonicida from infected salmon was 105-108 cfu/fish/hr. Survival and shedding results were combined in a computer model. A. salmonicida was predicted to travel >6 km suspended within the water column of a sea loch. Covert infection in freshwater farmed salmon was assessed by ELISA and the standard stress test. Results indicated that ELISA may be useful as a routine monitor of furunculosis infection. The efficacy of dot-blot immunoassay was found to be 108 cfu A. salmonicida in fish kidney tissue. Rainbow trout (Oncorhynchus mykiss) and salmon mucus were not found to inhibit the growth of A. salmonicida supporting recent evidence that fish skin is a site of carriage. In vitro studies suggested that trout serum proteins do not confer protection from fish antibody on A. salmonicida in covert infections. Preliminary work was undertaken to develop a specific DNA probe for A. salmonicida which will allow its detection in environmental samples and carrier fish. A gene library of A. salmonicida was constructed in lambda gtll and screened for "A"-protein with antibodies.

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains vi, 93 p. : ill. Vita. Includes abstract. Includes bibliographical references.

University, Diss., 2004--Konstanz. / Erscheinungsjahr an der Haupttitelstelle: 2003.

Aeromonas salmonicida is associated with superficial skin infections in fish. Its virulence factors allow colonization of water including surface water such as salt water, beaches, and fresh water wells. Moreover, it is possible for immunocompromised patients to develop invasive disease after chronic exposure to Aeromonas spp.Through contaminated water. While there are reports of Aeromonas spp. bacteremia following water ingestion, there have been no reports of A. salmonicida bacteremia from water consumption. We report the first case of A. salmonicida bacteremia in a patient with diabetes due to chronic consumption of well water.

Aeromonas salmonicida ssp. salmonicida est l'agent étiologique de la furonculose chez les salmonidés, spécialement les poissons d'élevage. Les pertes économiques pour l'aquaculture au Québec liées à cette maladie sont considérables. En raison des traitements par antibiotiques, on observe une émergence de souches d'A. salmonicida ssp. salmonicida résistantes aux antibiotiques. C'est pourquoi différentes alternatives, dont la vaccination, sont étudiées afin de prévenir la furonculose. Généralement, les vaccins utilisés injectent des bactéries mortes. En revanche cette méthode peut être laborieuse et inefficace. Ce projet s'intéresse au développement de souches vivantes atténuées qui pourraient être utilisées comme vaccin dans les piscicultures. Des études antérieures ont démontré que la virulence de la bactérie pouvait être atténuée lorsqu'exposée à un stress. Cela est expliqué par la perte des gènes du système de sécrétion de type trois (SSTT), qui ont un rôle essentiel dans la virulence de la bactérie. Cependant, le mécanisme reste encore inconnu et conséquemment, ce projet avait comme principal objectif d'identifier et caractériser les différents éléments génomiques pouvant contribuer à l'instabilité du SSTT. Tout d'abord, plusieurs souches d'A. salmonicida ssp. salmonicida ont été cultivées à 25 °C, ce qui est supérieur à leur température optimale de 18 °C. Les résultats ont révélé que certaines souches pouvaient perdre leur SSTT, mais que d'autres étaient réfractaires à la délétion des gènes malgré leur exposition à un stress. Une analyse génomique de ces différentes souches a permis d'identifier la présence d'un regroupement de gènes qui semble jouer un rôle dans l'instabilité du SSTT. Ces gènes sont retrouvés en majorité chez les souches sensibles et ils sont absents pour les souches réfractaires. Ce regroupement de gènes sera étudié en vue de créer des souches atténuées à partir de souches réfractaires. Ces souches seront ensuite testées sur les poissons pour déterminer l'efficacité de cette approche vaccinale contre la furonculose. / Aeromonas salmonicida ssp. salmonicida is the causative agent of furunculosis in salmonids, especially in farmed fish. The economic losses for aquaculture in Quebec related to this disease are considerable. As a result of antibiotic treatments, there is the emergence of antibiotic-resistant strains of Aeromonas salmonicida ssp. salmonicida. This is why different alternatives, including vaccination, are being studied to prevent furunculosis. Historically, the vaccines used are composed of dead bacteria. However, this method can be laborious and inefficient. This project is interested in the development of live attenuated strains that could be used as a vaccine in fish farms. Previous studies have shown that the virulence of the bacteria can be reduced when exposed to stress. This is explained by the loss of the genes of the type three secretion system (TTSS), which is essential in the virulence of the bacteria. However, the mechanism is still not fully understood and consequently the main objective of this project was to identify and characterize the different genomic elements that can contribute to the instability of TTSS. First, several strains of A. salmonicida ssp. salmonicida were grown at 25 °C, which is above their optimum temperature of 18 °C. The results revealed that some strains could lose their TTSS, but others were resistant to gene deletion despite their exposure to stress. Genomic analysis of these different strains identified the presence of a cluster of genes that appears to play a role in the instability of TTSS. These genes are found mostly in sensitive strains and they are absent in refractory strains. This cluster of genes will be studied to create attenuated strains from refractory strains. These strains will then be tested on fish to determine the effectiveness of these strains as a vaccine approach against furunculosis.