199株猪链球菌临床分离株血清型、毒力基因及多位点序列分型分析

【背景】猪链球菌（Streptococcus suis，SS）血清型、基因型众多，毒力因子复杂。【目的】了解SS临床分离株血清型、毒力基因分布、分子分型特征及其之间的相关性。【方法】针对199株SS临床分离株，应用PCR技术进行血清分型和毒力基因检测，采用多位点序列分型方法（multilocus sequence typing，MLST）进行基因分型，并分析SS血清型、毒力基因型和序列型（sequence type，ST型）的流行特点及其关联性。【结果】199株SS临床分离株分属于16种血清型（1、2、3、4、6、7、8、9、10、12、15、16、21、24、29和30型），主要以2、4、3型为主，分别占26.13%（52/199）、14.57%（29/199）和12.06%（24/199），未定型（NT）菌株占21.61%（43/199）。共鉴定出72种ST型，其中ST1、ST94、ST117、ST7、ST28和ST87为主要ST型，分别占12.56%（25/199）、11.56%（23/199）、9.56%（19/199）、9.04%（18/199）、6.03%（12/199）和3.01%（6/199），另有24种新发现的ST型（ST1224—ST1227，ST1229—ST1235，ST1241—ST1242，ST1300—ST1310）；分为12个克隆群（cloning complexes，CC）和32个单个ST型。199株SS分离株中毒力基因fbps的检出率最高，为96.98%（193/199）；共有19种毒力基因型，其中66株（33.17%）epf-/mrp-/sly-/gapdh+/fbps+/orf2+型SS为优势毒力基因型。【结论】近年来SS的优势血清型为2、4和3型；ST型具有明显的遗传异质性，种内分化程度较高且与ST型存在一定交叉性；毒力基因分布情况存在差异，毒力基因型呈现多样化。本研究对SS临床分离株的流行特征进行探究，为猪SS病诊断、治疗和制定防控措施提供科学依据。

Serotypes, main virulence genes, and multilocus sequence typing of 199 clinical isolates of Streptococcus suis

Background] Streptococcus suis (SS) has a variety of serotypes, genotypes, and virulence factors. Objective] To reveal the serotypes, virulence gene distribution, molecular typing characteristics and their associations of SS clinical isolates. Methods] A total of 199 clinical isolates of SS were collected in this study. We employed PCR to detect the serotypes and virulence genes and carried out multilocus sequence typing (MLST). Further, we analyzed the prevalence and associations of serotypes, virulence genotypes and sequence types (STs). Results] The 199 SS clinical isolates belonged to 16 serotypes (1, 2, 3, 4, 6, 7, 8, 9, 10, 12, 15, 16, 21, 24, 29, and 30). The serotypes 2, 4, and 3 were dominant, respectively involving 26.13% (52/199), 14.57% (29/199), and 12.06% (24/199) of the strains, and 21.61% (43/199) of the strains were untypable. We identified 72 STs, among which ST1, ST94, ST117, ST7, ST28, and ST87 were dominant, the strains of which accounted for 12.56% (25/199), 11.56% (23/199), 9.56% (19/199), 9.04% (18/199), 6.03% (12/199), and 3.01% (6/199), respectively. Twenty-four STs (ST1224-ST1227, ST1229-ST1235, ST1241−ST1242, and ST1300-ST1310) were newly discovered. In addition, these 72 STs involved 12 cloning complexes and 32 single STs. The detection rate of the virulence gene fbps in the 199 isolates was 96.98% (193/199). A total of 19 virulence genotypes were detected, among which epf‒/mrp‒/sly‒/gapdh+/fbps+/orf2+ were dominant (66 strains, 33.17%). Conclusion] In recent years the serotypes 2, 4, and 3 were dominant among the clinical isolates of SS. ST had obvious genetic heterogeneity and high degree of intraspecific differentiation. The serotypes and STs showed certain crossover. The isolates in this study presented varied distribution of virulence genes and diverse virulence genotypes. In this study, the epidemiological characteristics of SS clinical isolates were investigated to provide scientific basis for diagnosis, treatment and prevention and control measures of SS disease.