空肠弯曲菌群体遗传特征及菌型传播动力模型分析

Population genetic studies have an important role to play in the investigation of bacterial pathogens and have proved particularly informative in exploring the epidemiology of Campylobacter jejuni (C. jejuni). C. jejuni is a major foodborne pathogen and causes human gastroenteritis throughout the world. In addition to the burden of disease due to gastroenteritis, C. jejuni infection is highly associated with the development of Guillain-Barre Syndrome (GBS). With the rapid economical development, the increase of C. jejuni infection has a substantial public health and socioeconomic impact in China..C. jejuni has a widespread distribution with a broad range of animal hosts and environmental reservoirs. Food-producing animals such as poultry, cattle, and sheep commonly harbor vast numbers of C. jejuni isolates in their gastrointestinal tracts and represent an important route through which organisms could enter the food chain. However, the transmission dynamics of this infection are complex, and the relative contribution of different sources in C. jejuni infections has remained unclear in China. Recently, some molecular typing methods had been proven to be a valuable and robust characterization tools for C. jejuni and had provided useful information in epidemiological and population dynamic studies of this important pathogen. Molecular typing studies indicated that certain groups of related genotypes persist over time during geographical spread and a relative limited subset of them caused human disease and appeared to be associated with particular animal host. Recently, the use of mathematic models and the models which synthesize the population genetics and evolutionary processes, called phylodynamic model, is an effective way to quantify the pathogen transmission dynamics and source attribution. .Based on our previous investigation on the genome sequence and molecualr subtyping of C. jejuni, we plan to use some reliable and definitive molecular typing methods combined with the genome sequence analysis （genome structure, pan-genome and core genome analysis, SNP and evolution analysis, etc.）for C. jejuni isolates from a wide range of sources including food, animal, clinical patients and environment to obtain the genetic distribution, diversity and the population relationships of C. jejuni from China, to use the mathematic and phylodynamic models to investigate the sources attribution and transmission mechanism of C. jejuni in China. The proposed experiments will significantly enhance our understanding of the genetic characteristics, the sources attribution and the transmission dynamics of C. jejuni in China.

病原菌群体遗传研究对于探索其致病机制以及流行特征具有重要意义。空肠弯曲菌是主要的食源性病原菌，在欧美等经济发达国家，其感染位于食源性病原菌感染首位。除肠炎外，空肠弯曲菌的感染可导致格林-巴利综合征，造成严重经济负担。随着经济的发展及生活方式的变化，我国空肠弯曲菌感染率显著升高，但其感染来源、传播机制，不同宿主内菌株的变异规律及菌型差异不明确，导致人类感染的主要菌型或克隆不确定，不同菌型或克隆在不同宿主间的传播机制，传播动力等缺乏研究数据。本研究拟在前期研究的基础上，采用细菌分子分型，毒力相关基因序列分析与菌株基因组序列分析（基因组结构、SNP变异以及同源基因及进化分析等）相结合的手段，获得我国不同宿主来源菌株的遗传特征、变异规律；根据不同宿主菌型(群)分布特点，采用数学统计与菌型变异动力模型相结合手段，探讨病原菌的宿主归因及传播动力特点，为我国空肠弯曲菌感染的防控提供理论依据和技术手段。

病原菌群体遗传研究对于探索其致病机制以及流行特征具有重要意义。空肠弯曲菌是主要的食源性病原菌。除肠炎外，空肠弯曲菌的感染可导致格林-巴利综合征，造成严重经济负担。我国空肠弯曲菌感染率显著升高，但其感染来源、传播机制，不同宿主内菌株的变异规律及菌型差异不明确。本研究收集菌株1200株，完成脉冲场凝胶电泳（PFGE）分析1000余株、完成777株弯曲菌的多位点序列分型（MLST）分析。获得我国不同地域、不同宿主来源菌株菌型分布特征。通过基于序列特征的遗传相关性分析，确定我国不同宿主来源空肠弯曲菌呈分散分布，而80%以上的结肠弯曲菌为ST-828克隆群。通过对300余株空肠弯曲菌的重要毒力相关基因簇荚膜多糖（CPS）的遗传特征分析，确定菌株CPS合成相关基因簇与菌株的血清型密切相关，相同血清型的CPS基因簇序列一致，不同血清型有特异的遗传序列特征。据此，本研究建立了针对不同血清型及CPS特征的多重PCR的检测方法，并完成我国分离菌株的筛查。.本研究完成29株空肠弯曲菌的的基因组的测序，通过对包括NCBI发表序列的供168株弯曲菌基因组水平的Core-,Pan- 基因分析以及core-genome SNPs分析，确定不同来源菌株的遗传相关性，我国不同来源空肠弯曲菌分散分布在世界各地不同来源的菌株聚类组群中，但导致格林-巴利综合征的菌株呈一定程度的聚类特征。通过结肠弯曲菌的7个管家基因外，进行mampA ，flaA-SVR，PorA等特异基因的序列分析，确定我国结肠弯曲菌呈现聚类特征，CC828是我国菌株的主要克隆群。.以ST的序列型为参数，使用Arlequin软件包进行不同宿主群体菌株的分子方差分析（AMOVA）和固定指标（FST）的分析，确定家禽来源的菌株种群与腹泻患者来源菌株的遗传距离最近。使用Structure软件的贝叶斯归因模型对中国临床弯曲菌进行宿主归因,确定中国空肠弯曲菌临床株主要来源鸡（52.3%），其次分别为家畜（29.2%）和水禽（18.5%）来源。中国结肠弯曲菌临床株主要来源为猪（71.5%），其次为鸡（28.5%）。获得我国弯曲菌的宿主归因及传播特点，为我国空肠弯曲菌感染的防控提供理论依据和为我国弯曲菌感染的风险评估提供了技术手段。