Salmonella is a Gram-negative bacterium that consists of two species; S. enterica and S. bongori. The species S. enterica can be further divided into 6 subspecies and subspecies I is predominantly associated with disease in warm blooded animals and contains over 2,500 antigenically distinct serovars. Each serovar is >90% identical at the DNA level but can infect a different range of hosts and cause different diseases. Poultry are an important reservoir of entry of Salmonella into the human food chain owing to the contamination of their eggs and meat. The molecular mechanisms underlying colonisation of food producing animals with Salmonella are unknown. Fimbrial genes encode proteinaceous surface exposed appendages which have been shown to mediate adhesion of bacterial cells but the precise role for fimbriae in the carriage and virulence of Salmonella is poorly defined. The purpose of this study was to annotate and characterise the fimbrial genes of the poultry-associated S. enterica serovars Enteritidis and Gallinarum and relate this role to host-specificity. The availability of the genome sequences of several strains of S. enterica allowed a comparison of the sequence, location and repertoire of fimbrial genes and although no unique fimbrial genes were identified all serovars possessed a unique repertoire. The host-specific serovars contain a higher number of pseudogenes within fimbrial operons than the ubiquitous serovars and the rate of attrition of fimbrial genes was 3-4 fold higher than the genomic mean. Such gene decay may partially explain the narrowing of host-range of the host-restricted and host-specific serovars. Polymorphisms that may alter transcription were identified along with targets that may be associated with phase variation of the fimbrial genes. Lambda red-mediated homologous recombination was used to construct a panel of S. Enteritidis P125109 and S. Gallinarum 287/91 strains lacking major fimbrial subunit genes which were examined in vitro and in vivo. Several fimbrial subunits played a role in the adherence to and invasion of different cell lines in different growth conditions and the role appeared to be serovar-specific. A mutation in the steA gene impaired interactions with different cell lines in vitro but this phenotype was found to be due to a polar effect on genes downstream of steA. The majority of fimbrial subunits played no significant role in the colonisation of the alimentary tract in an established chicken model. Mutation of the stcA gene resulted in the greatest degree of attenuation in vivo of all of the fimbrial mutants examined. This phenotype was trans-complemented and was not the result of a polar or second-site defect thereby fulfilling molecular Koch’s postulates. The stcA genes therefore play a significant role in the colonisation of the chicken caeca.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:500270 |
| Date | January 2008 |
| Creators | Clayton, Debra Jayne |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/4200/ |
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