A molecular Investigation of campylobacter jejuni pathogenesis

Lodge, K 2007, A molecular Investigation of campylobacter jejuni pathogenesis, Doctor of Philosophy (PhD), Applied Sciences, RMIT University.


Document type: Thesis
Collection: Theses

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Title A molecular Investigation of campylobacter jejuni pathogenesis
Author(s) Lodge, K
Year 2007
Abstract Campylobacter jejuni is one of the leading bacterial causes of human gastroenteritis world wide and has been linked to several severe complications including autoimmune syndromes which can result in paralysis. Despite being the subject of much study, C. jejuni remains a major public health burden in both developing and developed nations. There is currently no vaccine available for protection against this pathogen and the mechanisms important for C. jejuni pathogenesis are not fully defined.

This study has employed a range of experimental approaches to investigate the molecular mechanisms involved in C. jejuni pathogenesis. Lipooligosaccharides (LOSs) are surface structures and known virulence factors of C. jejuni which are involved in serum resistance, resistance to phagocytic killing, endotoxicity and adhesion. Mutagenesis studies targeting the putative LOS biosynthesis genes wlaRF, wlaTA, wlaTB, wlaTC and waaV were performed in order to characterise the proteins encoded by each of these six genes and assess their potential role in C. jejuni pathogenesis in vitro.

The gene product of wlaTA was found to be essential for C. jejuni survival and therefore a knock out mutant could not be generated. Phenotypic characterisation of four knock-out mutants confirmed that each gene contributed to the construction of the LOS molecule as all four mutants produced a truncated LOS moiety and altered their immunoreactivity. Further analysis determined that the production of complete LOSs was important for C. jejuni to invade and adhere to both human and chicken cells in vitro.

This study identified a link between the inactivation of two LOS biosynthesis genes and the loss of motility, another important virulence factor. A major source of human C. jejuni infection is contact with contaminated poultry. However, C. jejuni exists as a commensal in chickens. It is currently not known why C. jejuni is pathogenic to humans and not to chickens and the differences between these two hosts represent pathogenic and non-pathogenic environments respectively. These environmental differences were exploited in this study.

The four conditions investigated were temperature, blood, bile and host cells in vitro. Five different C. jejuni strains (NCTC11168, 81116, HB93-13, a recent human enteritis isolate and a recent chicken isolate) were subjected to modelled "chicken" or "human" environments. Six differentially expressed surface proteins were identified by MALDI-TOF. The environmentally regulated proteins included a transthyretin-like protein (Cj0715), a protein involved in iron uptake (p19), a hypothetical periplasmic protein (Cj0998c), the adhesin PEB1, flagellin A and the major outer membrane protein.

The purpose of this study was to investigate the pathogenesis of C. jejuni at a molecular level. The outcomes of this work include the characterisation of genes that encode proteins involved in the construction of a known virulence factor, LOS, the link of these genes to another known virulence mechanism, that is motility and the identification of six surface proteins which may be important in how C. jejuni causes disease in humans. The enhanced understanding of the molecular mechanisms important for the pathogenesis of C. jejuni, will expedite the development of successful antimicrobial therapies or vaccines to control or prevent infection.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Sciences
Keyword(s) Viral gastroenteritis
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