Determining how phase variation contributes to host colonisation and extraintestinal spread of Campylobacter jejuni

Campylobacter jejuni is the major causative agent of foodborne gastroenteritis across Europe. Contaminated chicken meat is the main source of infections and hence control of this pathogen is critical to food security in the poultry industry. This bacterial species has three major virulence determinants; capsule, lipooligosaccharide (LOS) and flagella. The flagella mediate motility of this bacterial pathogen enabling movement towards nutrients and away from damaging agents. The capsule and LOS mediate resistance to immune effectors, influence adhesive properties and contribute to autoimmune complications of C. jejuni infections. All three components are decorated with a variety of sugar molecules (glycans). These glycans are highly variable between strains due to differences in gene content and allelic variation. Many of these glycans also vary in structure and presence within strains due to high frequency, reversible switches in gene expression caused by hypermutable sequences and referred to as phase variation (PV). As part of a recent BBSRC-funded project grant, phase-variable genes were found to exhibit directional changes during colonisation of chickens and extraintestinal spread. Samples were derived from two large-scale chicken infection studies with four C. jejuni lineages, multiple isolates and four sample sites (caecal contents, ileal contents, spleen and liver). Only single-gene expression states have been examined in detail whereas multi-gene expression states have the potential to allow for detection of co-selection of PV genes, bottlenecks and sources of extraintestinal spread (e.g. caeca or ileum). In this project, it is hypothesised that phase variation contributes to colonisation and extraintestinal spread of C. jejuni within the chicken host. This project will examine data for combinatorial PV expression state changes. The contributions of specific PV genes will be assessed by constructing mutants in LOS, capsular or outer membrane protein PV genes to associate specific PV changes with specific types of phenotypic variation. Mathematical models will also utilise PV data to examine the dynamics of colonisation and extraintestinal spread. Overall this project will provide insights into how C. jejuni colonises and spreads within chicken and identify potential points of interference that could prevent this source of C. jejuni gastrointestinal infections.