Characterization of the emerging zoonotic pathogen <i>Arcobacter thereius</i> by whole genome sequencing and comparative genomics

Four Arcobacter species have been associated with human disease, and based on current knowledge, these Gram negative bacteria are considered as potential food and waterborne zoonotic pathogens. At present, only the genome of the species Arcobacter butzleri has been analysed, and still little is known about their physiology and genetics. The species Arcobacter thereius has first been isolated from tissue of aborted piglets, duck and pig faeces, and recently from stool of human patients with enteritis. In the present study, the complete genome and analysis of the A. thereius type strain LMG24486T, as well as the comparative genome analysis with 8 other A. thereius strains are presented. Genome analysis revealed metabolic pathways for the utilization of amino acids, which represent the main source of energy, together with the presence of genes encoding for respiration-associated and chemotaxis proteins. Comparative genome analysis with the A. butzleri type strain RM4018 revealed a large correlation, though also unique features. Furthermore, in silico DDH and ANI based analysis of the nine A. thereius strains disclosed clustering into two closely related genotypes. No discriminatory differences in genome content nor phenotypic behaviour were detected, though recently the species Arcobacter porcinus was proposed to encompass part of the formerly identified Arcobacter thereius strains. The report of the presence of virulence associated genes in A. thereius, the presence of antibiotic resistance genes, verified by in vitro susceptibility testing, as well as other pathogenic related relevant features, support the classification of A. thereius as an emerging pathogen.已有四种弓形杆菌属（Arcobacter）物种与人类疾病相关，根据现有认知，这类革兰氏阴性菌（Gram negative bacteria）被视为潜在的食源与水源性人畜共患病原体（zoonotic pathogens）。目前仅对布氏弓形杆菌（Arcobacter butzleri）的基因组（genome）完成过分析，学界对其生理与遗传特性的了解仍十分有限。泰氏弓形杆菌（Arcobacter thereius）最初从流产仔猪组织、鸭组织及猪粪便中分离得到，近期又从肠炎患者的粪便样本中被分离出。本研究报道了泰氏弓形杆菌模式菌株（type strain）LMG24486^T的完整基因组及分析结果，同时对另外8株泰氏弓形杆菌菌株开展了比较基因组分析（comparative genome analysis）。基因组分析结果显示，该菌存在以氨基酸为主要能量来源的代谢通路（metabolic pathways），同时携带编码呼吸相关蛋白与趋化蛋白的基因。与布氏弓形杆菌模式菌株RM4018的比较基因组分析显示，二者存在高度相关性，但也存在各自独特的特征。此外，对9株泰氏弓形杆菌的计算机模拟DNA-DNA杂交（in silico DDH）与平均核苷酸一致性（ANI）分析结果表明，这些菌株可聚类为两种紧密相关的基因型（genotypes）。尽管近期有研究提议将猪弓形杆菌（Arcobacter porcinus）纳入此前部分被鉴定为泰氏弓形杆菌的菌株，但未在基因组内容与表型特征中检测到显著差异。本研究发现泰氏弓形杆菌携带毒力相关基因（virulence associated genes），经体外药敏试验（in vitro susceptibility testing）验证其存在抗生素抗性基因（antibiotic resistance genes），以及其他与致病性相关的关键特征，上述结果均支持将泰氏弓形杆菌归类为一种新兴病原体（emerging pathogen）。