Campylobacter Jejuni virulence mechanisms : characterisation and regulation
thesisposted on 15.12.2014, 10:38 by Ana Maria Leao da Silva. Bras
Campylobacter jejuni is a major cause of gastrointestinal illness throughout the world. Despite its importance as a human pathogen, the current understanding of C. jejuni virulence mechanisms or the means by which the bacterium regulates the expression of virulence remains limited. In this thesis, two different areas were investigated and are presented separately. In Part I, studies focused on the characterisation of C. jejuni translocation across an epithelial-like barrier. It was previously demonstrated that many strains of C. jejuni are able to translocate across polarised Caco-2 cell monolayers. A small number of these strains are not detectable within cells but are nevertheless able to translocate across the monolayer, presumably using a paracellular route. The possibility of paracellular translocation (without invasion) was investigated by looking at changes in the permeability across differentiated Caco-2 cell monolayers. The data obtained suggest that C. jejuni does not significantly alter the permeability of the monolayer, causing no permanent damage to the host cells, at least in the short term. In the long term, however, C. jejuni infection leads to a drop in the monolayer resistance, suggesting host cell damage. Although paracellular translocation seems unlikely to occur in the early stages of infection, it may occur later as consequence of host cell damage caused during invasion. In Part n, studies focused on the role played by the environment on the regulation of C. jejuni virulence. Two-component regulatory systems are involved in the regulation of numerous cell functions in response to environmental stresses, including virulence. Recently, the polymerase chain reaction with degenerate oligonucleotide primers was used to isolate regulatory genes responsive to environmental stimuli. The fragment isolated was identified as homologous to the members of the family of response regulators. The DNA fragment was subsequently used to probe a genomic library. The complete gene, regXl, was isolated, sequenced and mutated. In order to determine the role of regXl in C. jejuni, the phenotype of two regXl mutants was investigated. The results suggest that RegXl may respond to changes in temperature and that RegXl may be involved in the control of genes related to growth, host cell interaction and in vivo colonisation. Furthermore, a putative histidine protein kinase partner to RegXl was identified downstream regXl.