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Title: Genomic variation in the zoonotic pathogen Campylobacter jejuni
Author: Hepworth, Philip John
ISNI:       0000 0004 2670 9536
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2008
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The zoonotic bacterium Campylobacterjejlllli is the major cause of gastrointestinal disease in developed countries. The source ofhuman infections is believed to be animal food products, but the relative contributions ofdifferent sources to the overall burden of disease remain unclear. By improving our knowledge ofthe variable genome of Campylobacterjejlllli it may be possible to uncover links between variable gene distribution and strain phenotypes such as host preference or virulence. Our current knowledge ofvariable genes may be unrepresentative of strains from potential disease reservoirs such as ruminants and wildlife species. The technique of suppression subtraction hybridization can be used to identify gene fragments present in the genome of a strain of interest (tester strain) but absent from the genome ofa reference strain (driver strain). We carried out subtractions using strains from novel hosts, and various MLST clonal complexes. The distribution ofeight subtracted sequences was analysed using PCR and dot blot hybridization. These sequences included four with putative roles in the use of alternative electron acceptors, which have been hypothesized to contribute to selective advantages in specific ecological niches. For these eight subtracted sequences there was no evidence for a link between sequence distribution and host species. However, there was a clear correlation between subtracted sequence distribution and clonal complex, suggesting minimal transfer ofthese genes between clonal complexes. To further characterise genomic variation in C. jejzl11i populations, comparative genomic hybridization was carried out on a panel of C. jejlllli isolates representing diverse host species and MLSTs. DNA from these isolates was interrogated using a newly developed oligonucleotide microarray based on the genomes of C. jejllni strains NCTC11168, RM1221 and 81-176. The microarray also included strain variable genes from other strains and genetic loci in the database, and a selection of genes from our subtractions. The strain panel included several isolates from wildlife and water sources with unusual MLST genotypes not currently found in clinical isolates from humans (WW isolates). . Clustering analysis ofM-CGH data confirmed that genomic content was assocfated with the MLST rather than the host species ofthe isolates. Strikingly the WW isolates had a number of genes deleted or significantly divergent from the arrayed genes, which were present in all or most other isolates. Many ofthese genes had functions which related to colonisation, invasion and virulence. This suggests that the WW strains may reach humans but may be unable to colonise or cause disease in humans. The genome sequence of a WW isolate revealed several novel genomic insertions not present in the genome of C. jejzl11i NCTC11168. These novel insertions may contain genes which contribute to the colonisation of water and wildlife sources, or the unusual epidemiology of the WW strains. Further studies will include the genome sequencing of several more WW isolates and characterisation oftheir colonisation phenotypes using a chick colonisation model, expression M-CGH, and defined gene mutants.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral