Abstract
The purpose of the following studies was to Micrographics. investigate the virulence and mechanisms of prevention of Salmonella gallinarum (SG) in the commercial poultry. Salmonella gallinarum is a pathogen that is strongly adapted to fowl and aquatic birds but exactly how the genetic makeup of this host restricted pathogen differs from that of broad host range serotypes, such as the well studied ST, is not known. In order to survey the repertoire of virulence genes in SG, a total of 341 different mini-Mu transposes mutants were generated and used as a sample which represented an estimated 7.7% of the genome using the assumption that the sample was random. Virulence of each individual mutant was assessed by oral infection of chicks and eleven mutants were found not to cause mortality. This data inferred that the total number of genes required to cause lethal disease in chicks is approximately 120. Our preliminary results on sequence analysis of DNA flanking the transposes insertion in attenuated mutants suggest that about half of the virulence genes identified in SG are not present in Escherichia coli (EC) and may thus have been obtained by way of horizontal gene transfer. To further investigate mechanisms of preventing SG organ invasion and colonization, the interaction of dexamethasone (DEX) and lipopolysaccharide (LPS) was evaluated in an organ invasion assay. The combination of DEX and LPS resulted in an 85% decrease in organ invasion as compared to controls. This suggests that DEX+LPS may be a beneficial method for the reduction of Salmonella organ invasion in chicks and as worthy of further study.
Edwards, Emmerson Wendell (1998). Identification of mechanisms of Salmonella gallinarum virulence. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1998 -THESIS -E33.