Browsing by Subject "virulence"
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Item Characterization of emerging Brachyspira pathogens in swine: Applications to disease control(2016-12) Mirajkar, NanditaSwine dysentery (SD) is a mucohemorrhagic diarrheal disease of pigs and is a welfare and economic issue globally. Its re-emergence in the U.S. after two decades of quiescence was associated not only with B. hyodysenteriae but also with a novel spirochete, Brachyspira hampsonii. The overall objective of this dissertation was to determine the genotypic, antimicrobial susceptibility and virulence factors of these pathogens in order to understand the re-emergence of SD in the U.S. As the re-emergent isolates were genetically related to historic isolates, it is likely that B. hyodysenteriae persisted in the U.S. over the last two decades without causing overt clinical disease. B. hampsonii isolates from migratory birds and pigs were found to be closely related, thus highlighting the potential role of migratory birds in its emergence in swine herds. When the broth microdilution method was compared with the agar dilution/strip test methods for antimicrobial susceptibility testing (AST) of various Brachyspira species, with the exception of carbadox, all other evaluated antimicrobials (tiamulin, valnemulin, lincomycin, tylosin and doxycycline) showed high agreement between the methods. Most Brachyspira isolates demonstrated high susceptibility to tiamulin, valnemulin and carbadox, heterogeneous susceptibility to doxycycline and low susceptibility to lincomycin and tylosin. Decreased tiamulin susceptibility, when rarely identified, was associated with the genotype, stage of production and production system from which the isolate originated, possibly reflecting local antimicrobial usage. Overall, antimicrobial resistance did not seem likely to be the cause of the re-emergence of SD in the U.S. The genomic comparison of U.S. B. hyodysenteriae field isolates revealed several mobile elements that showed variation between the isolates and are likely associated with the evolution of this species. Genes involved in carbohydrate and cell wall biosynthesis, cell survival and host-pathogen interaction were predicted to be potentially associated with B. hyodysenteriae virulence. Based on a comprehensive polyphasic approach (multiple whole-genome comparison, genotypic and phenotypic data), Brachyspira hampsonii sp. nov. was classified as a unique species with genetically diverse yet phenotypically similar ‘genomovars’. Finally, this work also provided information that can directly (genotyping, ASTs) and indirectly (gene candidates for diagnostic tests and vaccines) be applied to disease control.Item Identification of Cochliobolus sativus isolates expressing differential virulence on two-rowed barley genotypes from North Dakota(Canadian Journal of Plant Pathology, 2009-12-29) Fetch Jr, T.G.; Steffenson, BrianSevere spot blotch infection was observed in 1990 on several two-row barley breeding lines previously regarded as resistant to Cochliobolus sativus. Studies were conducted to compare the virulence pattern of a C. sativus isolate (ND90Pr) obtained from this two-row breeding nursery with one (ND85F) used in previous disease screening evaluations. Greenhouse and field experiments were performed in 1991 and 1992 at Fargo, ND, using a split plot design with isolate as the main effect. Isolates ND90Pr and ND85F exhibited distinct differential virulence patterns on barley genotypes ND 5883, ND 12437, ND 12720, ND 12721, and Bowman. Isolate ND90Pr displayed high virulence on ND 12720, ND 12721, and Bowman, and low virulence on ND 5883 and ND 12437. In contrast, isolate ND85F was highly virulent on ND 5883 and ND 12437 and weakly virulent on ND 12720, ND 12721, and Bowman. Both isolates expressed low virulence on genotype ND Bl 12, the primary source of resistance to C. sativus in commercial six-row barley germplasm. To incorporate adequate levels of resistance into future two-row barley cultivars, disease evaluations should be made with C. sativus isolates that express the full spectrum of virulence found in North Dakota.