Functional Characterisation of a Campylobacter Flagellin Glycosylation Island Important in Avian Adaptation

Campylobacter jejuni is the principal bacterial cause of human gastroenteritis worldwide. The main source of transmission is the consumption and handling of contaminated poultry, but the underlying reasons why most chickens are particularly susceptible to colonisation by C. jejuni are unknown. <P>

To investigate genetic determinants in C. jejuni that are involved in this process, we compared the genomes of 91 C. jejuni strains of diverse origin. The resulting phylogenetic tree was made up of two distinct clades - one comprising the chicken-associated strains, and one comprising the strains that were not chicken-associated. We found that the most prominent genetic marker shared by the chicken-associated strains was a cluster of six genes within the O-linked flagellum glycosylation locus (coding sequences cj1321 to cj1326). It is known that flagellin glycan structures, which are exposed on the cell surface, are important in determining the immune response of the host - they have been found to be immunodominant in C. jejuni and to be important in host specificity in other bacterial pathogens. <P>We hypothesise that the cj1321-26 island enables C. jejuni strains that possess it to persist in poultry, by encoding a specific glycoform of the flagellin that plays an integral role in the bacterium's interaction with its avian host. The presence of variant flagellin glycoforms encoded by this island may confer a combination of altered properties relating to colonisation, survival and immune response. <P>To investigate this hypothesis, we propose to thoroughly characterise the genetics, structure, function and immunology of the O-linked flagellin modification system in C. jejuni 11168H, including the newly identified cj1321- 26 island.<P> First, we will mutate and complement each of the six genes in the cj1321-26 glycosylation island, as well as generating defined and spontaneous deletion mutants of the island. <P>We will then carry out studies to test the ability of the different strains to colonise and survive in chickens, as well as histological and avian immune response studies. To test whether selective pressure is required to maintain the cj1321-26 glycosylation island in the avian host, we will compare the rate of spontaneous loss of the island in vitro and in vivo. To assess how the cj1321-26 genes affect cell surface properties and may be relevant in human disease, we will test the mutants in a range of in vitro assays including hydrophobicity, autoagglutination, serum resistance, motility, biofilm formation and bile salt resistance.<P> We will also test the parent and mutant strains ability to adhere to and invade CaCo2 human tissue culture cells, as well as their ability to trigger human innate immune and cytokine responses. In addition, we will use NMR and mass spectroscopy to determine the structure of the flagellin glycan in the parent 11168H strain and in each of the mutants.<P> This research programme will improve our understanding of the interactions between Campylobacter and chickens, and may make it possible to select chickens that are less susceptible to colonisation by this bacterium. In the longer term, this approach will help inform strategies to reduce C. jejuni from the food chain. Joint with BB/D521965/1.