Rubinchik, Sona (2015) The development and application of an ' in vitro ' model of ' Campylobacter jejuni ' interaction with host cell receptors. (PhD thesis), Kingston University, .
Abstract
Campylobacter jejuni is the most common cause of acute bacterial gastroenteritis in humans worldwide. Adhesion to the host cells is an important stage in pathogenesis of C. jejuni infection. It was hypothesised that some N-linked glycosylated proteins might be involved in bacterial attachment via interaction with lectins located on the surface of host cells. Glycan moieties of such glycoproteins contain terminal N- acetylgalactoseamine (GalNAc) residues that are specific to soybean agglutinin (SBA) lectins that are analogues of host cell receptors. C. jejuni is also known to express capsule, the role of which in adhesion still remains unknown. The main aims of this project were to investigate the putative glycoprotein adhesins of C. jejuni and the involvement of capsule in bacterial adhesion. In this study an in vitro assay was developed to assess bacterial adhesion to immobilised analogues of host cell receptors. This assay was used to verify the binding mechanism of C. jejuni through competitive inhibition studies, exoglycosidase treatment and site-directed mutagenesis, with the C. jejuni strain 11168H and its isogenic mutants. Results obtained in this study demonstrated that PEB3 is one of the cell surface glycoproteins involved in bacterial interaction with an analogue of a host cell receptor and that the presence of capsule reduces bacterial attachment. In addition, it was demonstrated that the presence of the glycoprotein adhesin JlpA is not required for this interaction. It was also shown that the genes involved in capsule and PEB3 adhesin biosynthesis are differentially regulated, suggesting that capsule and adhesins may be expressed at different stages of infection. Based on these results we hypothesise that capsule may be required for preventing the recognition of adhesins by the host immune system at the initial stages of infection. Following this initial evasion of the host immune response, the genes for capsule production may be down-regulated, leading to reduction in capsule production and the resulting exposure of cell-surface adhesins and cell surface molecules required for attachment and/or modulation of the host immune response. Additionally, a recombinant Escherichia coli strain expressing lipopolysaccharide (LPS) modified with a Campylobacter glycan was shown to inhibit binding of C. jejuni cells to SBA lectin. This finding may be used as the basis for the design of novel antibacterials using competitive inhibition as the mechanism of action. Overall, the results of this study will contribute to a better understanding of the pathogenic mechanism of C. jejuni infection and will help in the development of inhibitors of bacterial attachment to host cells. This will help to reduce the number of infections caused by C. jejuni and therefore reduce healthcare costs worldwide. Prevention of bacterial attachment or competitive inhibition used as a curative measure would therefore be beneficial to those in both developed and developing nations.
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