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Title: Genome sequence of the hyperinvasive Campylobacter jejuni strains
Author: Baig, A.
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2012
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Campylobacter jejuni is the world’s major cause of gastroenteritis in humans. Although motility, toxin production, adhesion and invasion are some of the key factors associated with C. jejuni pathogenesis, their mechanism in the disease process remains unclear. The key aim of this project is to study the genetic basis of hyperinvasiveness in a group of six C. jejuni strains which have been reported as hyperinvasive into human intestinal cell lines. Here, genomotyping of the hyperinvasive C. jejuni was performed by comparative genomic hybridization (CGH) against four low invasive C. jejuni strains. A group of 67 genes were identified as being present or highly divergent/absent in the hyperinvasive versus low invasive C. jejuni strains. Of these, nine genes were present and six genes were highly divergent/absent in all hyperinvasive C. jejuni. The PCR screening of these 15 genes in nine additional low invasive C. jejuni strains showed a significant association with the hyperinvasive phenotype. The majority of identified genes encoded proteins with essential cellular and metabolic functions along with some genes with known virulence related roles. Thus, the hyperinvasive phenotype is characterised by different functional networks rather than a single gene or gene cluster. All strains showed an overall genetic variability and the capsule, lipooligosaccharide, flagellar biosynthesis and restriction modification regions were the most diverse. The hierarchical clustering based on comparative genomic hybridization (CGH) did not group together the hyperinvasive C. jejuni as a single group and these strains possessed different MLST profiles. The hyperinvasive C. jejuni strains were shown to contain additional genetic content by pooled suppressive subtractive hybridization (PSSH). Eleven inserts were identified in total which were variably distributed in the hyperinvasive C. jejuni strains. Of these four sequences were specific to the hyperinvasive C. jejuni as these were absent from all thirteen low invasive C. jejuni strains tested. The majority of sequences matched with genes in Campylobacter and other bacteria and one sequence had no homology with anything in the databases today. Since, there is no insert identified as present in all the hyperinvasive C. jejuni strains it can be suggested that each strain might have evolved a different mechanism for hyperinvasiveness and that this phenotype is a multifactorial process. C. jejuni 01/10 and 01/51 whole genome sequences identified no unique genetic content in either strain except for a prophage in C. jejuni 01/51. C. jejuni 01/10 was found to contain two prophages. C. jejuni 01/51 has a highly mosaic capsule locus with genes similar to C. jejuni subsp. doylei and C. lari capsular polysaccharide genes. Some genes with homology to the C. jejuni subsp. doylei capsule genes were also identified in C. jejuni 01/10 capsule region. This is evidence of genetic recombination with capsule genes from other pathogenic Campylobacter species which is not reported in the capsule region of other Campylobacter strains sequenced to date. This suggests that the highly diverse capsule in C. jejuni 01/10 and 01/51 is required for the hyperinvasive phenotype in these strains. This study has provided detailed insight into the genomic structure of the hyperinvasive C. jejuni strains and has highlighted genetic factors involved in their hyperinvasive phenotype.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available