军团菌属（Legionella）系一种水环境中广泛存在胞内寄生菌，目前已有58个种，其中有25个种对人体致病，以嗜肺军团菌为主。 在嗜肺军团菌里血清型1型菌株的感染站所有感染病例的85%。目前已有众多军团菌系统分类与分子分型研究报道：如脉冲场凝胶电泳，扩增长度片段多态性，序列分析等。但这些军团菌分型方法，对同种不同来源菌株无法区分，如无法将临床来源嗜肺军团菌菌株与环境水样中分离到的菌株进行区分。因此，对军团菌分子遗传与系统分类以及嗜肺军团菌分型的进一步研究很有必要。.单核苷酸多态性（SNP）是指基因组上单个核苷酸发生变异引起的多态性。SNP分布广泛，在细菌中也广泛存在，并与细菌致病性、耐药性相关。SNP 所独有数量多、分布广、易于基因分型的特点，决定了它更适合于其他分型方法无能为力的复杂性状，以及同种细菌毒力标记的遗传解剖及识别分析。因此，对军团菌SNP研究及建立相关数据库将有助于军团菌系统分类和嗜肺军团菌分子分型，并为军团菌病控制提供帮助。

Legionella spp. are ubiquitous bacteria present in enviromental water systems. Inhalation of Legionella spp. in aerosolized water droplets from contaminated water sources is known to cause a type of pneumonia called Legionnaires’ disease (LD). To date, 58 Legionella species have been characterized, and 25 species are known to cause human disease. Legionella pneumophila is responsible for most of human infections and serogroup 1 alone accounts for almost 85% of cases. Several subtyping techniques including Pulsed-field gel electrophoresis (PFGE), Amplified fragment length polymorphism (AFLP) and Sequence-based typing (SBT) have been used to identify and characterize L. pneumophila strains. While, there have been some defections in these subtyping techniques (eg. Cannot distinguish clinical strains and envirronmental strarins). Therefore, further research on Legionella molecular genetics and developping more advanced stematics methods is needed..Single nucleotide polymorphism (SNP) refers to a single nucleotide mutation and polymorphism in the genome. SNPs are widely distributed in many species including bacteria, and are associated with bacteria virulence and antimicrobial resistance. The vast quantity, widely distribution of SNPs in the gnome of bacteria make it suitable for bacteria subtyping, especially those bacteria with complex trait and virulence factors. In the present study, we will research on more advanced systematics taxonomy methods of Legionella and molecular subtyping method for Legionella pneumophila based on the single nucleotide polymorphism of Legionella core gnome genes and virulence genes and compare it with SBT and muti-locus sequence typing. Our project is of great importance to bacterial evolution, pathogenic, pathogenic mechanism and outbreak control.