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

空肠弯曲杆菌是欧洲食源性胃肠炎的主要病原体。受污染的鸡肉是感染的主要来源，因此控制这种病原体对家禽业的食品安全至关重要。这种细菌有三个主要的毒力决定因素：衣壳、脂低聚糖(LOS)和鞭毛。鞭毛介导了这种细菌病原体的运动，使其能够向营养物质移动，而不是破坏性的物质。胶囊和LOS介导对免疫效应物的抵抗，影响粘附性，并导致空肠弯曲菌感染的自身免疫性并发症。所有这三种成分都装饰着各种糖分子(多糖)。由于基因含量和等位基因变异的不同，这些多糖在菌株之间是高度可变的。其中许多葡聚糖的结构和菌株内的存在也不同，这是由于超变序列引起的基因表达的高频、可逆开关，被称为相变(PV)。作为BBSRC最近资助的项目赠款的一部分，发现在鸡的定植和肠道外传播期间，阶段可变基因表现出方向性变化。样本来自两个大规模的鸡感染研究，包括四个空肠弯曲菌谱系、多个分离物和四个样本位置(盲肠内容物、回肠内容物、脾和肝脏)。只对单基因表达状态进行了详细研究，而多基因表达状态有可能检测到PV基因的共同选择、瓶颈和肠道外扩散的来源(例如盲肠或回肠)。在这个项目中，假设阶段变化有助于空肠弯曲菌在鸡宿主内的定植和肠道外传播。该项目将检查组合PV表达状态变化的数据。通过在LOS、囊膜蛋白或外膜蛋白PV基因中构建突变体，将特定的PV变化与特定类型的表型变异联系起来，来评估特定的PV基因的贡献。数学模型还将利用PV数据来检查定植和肠道外传播的动态。总体而言，该项目将深入了解空肠弯曲菌如何在鸡体内定植和传播，并确定潜在的干扰点，以防止空肠弯曲菌胃肠道感染的这一来源。

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.