Characterization of the embryo lethality assay, a pathogenic avian Escherichia coli isolate V1, and the discovery of arsH in Escherichia coli
Gibbs, Penelope S
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Colibacillosis in poultry causes massive losses to the industry due to the opportunistic nature of the disease and a lack of vaccines. Further research in pathogenesis will be required until successful vaccine regimes can be discovered. To accomplish this, an animal model must be available for evaluation of the virulence capabilities of individual isolates and related strains (i.e. isogenic strains with specific gene knockouts.) Our lab has implemented a chicken embryo model for assessing the virulence of avian E. coli isolates. Collaboration with the Statistical Consulting Laboratory in the Department of Statistics, Terry College of Business at the University of Georgia, resulted in a statistical analysis of the ELA using ten avian E. coli isolates from diseased birds as the “virulent” group, and ten avian E. coli isolates from the intestines of birds at slaughter as the “avirulent” group. While this analysis established repeatability and the ability of the assay to discriminate between isolates virulent in embryos and those that were not, the way in which the “virulent” and “avirulent” groups were defined left no room for comparisons of specific phenotypic and genetic traits between isolates. Some isolates from diseased birds were unable to kill a significant portion of the embryos, thus these isolates were prematurely include in the “virulent” group. We wanted to have the assay determine if the isolate was virulent, moderately virulent, or avirulent based on the ELA results. Additionally, we wanted to be able to predict the resulting embryo lethality of a given isolate based on evaluation of phenotypic and genotypic traits. |We also characterized a 56 kilobase pair plasmid, pWT3 purified from untypable avian pathogenic Escherichia coli isolate V1. Sequence analysis of cloned pWT3 fragments was used to predict possible ORFs and their homology with existing genetic information. DNA-DNA hybridization detection and PCR using primers specific for a region within the iss genetic system or the tsh gene, demonstrated the presence of several genes present in isolate V1 that have been associated historically with virulence in APEC, and a new gene, arsH, that was never before demonstrated within E. coli until now.