2005年广东省临床分离猪链球菌的MLST分子分型研究

MLST typing of Streptococcus suis isolated from clinical patients in Guangdong Province in 2005

在2005年四川发生猪链球菌人间感染疫情期间,广东省也加强了监测,并发现了5个散发感染病例。从这5个住院临床病例中,分别分离了5个致病性SS2。通过测定猪链球菌基因组上的7个看家基因dpr、thrA、cpn60、recA、gki、aroA和mutS的部分片段,对这5个猪链球菌进行了多位点测序分型。通过对上述测序片段进行比对分析发现,5个菌株的dpr、cpn60、recA、gki、aroA和mutS等6个基因片段完全相同;而thrA基因片段存在两个等位基因型即thrA-c和thrA-h,在该等位基因片段的360位的亮氨酸密码子第三位发生了一个中性突变(TTA→TTG)。MLST分析结果显示,广东省的临床猪链球菌分离株L-SS002、L-SS003和L-SS005菌株,与四川疫情株相同,属于ST7型;而L-SS004和L-SS006,与香港地区发现的猪链球菌相同,属于ST1克隆;但这5个菌株亲缘关系极近,都属于ST1克隆复合物;这一点与四川省暴发的人间猪链疫情明显不同,后者仅由单一的ST7猪链球菌克隆引起。属于ST7的克隆菌株很可能来源于四川;而其余两个ST1克隆系菌株的来源尚待鉴定。

Intensive surveillance of human S.suis infection was carried out in July and August of 2005 in Guangdong Province, which coincided with the Sichuan outbreak. Five isolated cases of human infections were identified during this period, from which 5S. suis serotype 2 isolates were recovered. MLST analysis showed that these 5 isolates shared identical sequences of 6 MLST housekeeping genes except for one point mutation found within the thrA gene fragment, a neutral mutation （TTA to TTG） in the third nucleotide （360 nt） of the codon for leucine. MLST analysis identified 2 sequence types in the Guangdong sporadic infection. Three Guangdong isolates L-SS002, L-SS003 and L-SS005 belonged to ST7, while the other two isolates L-SS004 and L-SS006 belonged to ST1, but they all belonged to ST1 clonal complex. This finding represents a striking feature that differs from the Sichuan outbreak caused by a single ST7 SS2 clone. The 3 isolates of ST7 were probably imported from Sichuan Province, while the origin of the other 2 isolates of ST1 still remain to be clarified.