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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。
During the outbreak of human infection of S. suis in Sichuan in 2005, Guangdong Province also stepped up surveillance and found five cases of infection. From the five in-hospital clinical cases, five pathogenic SS2 were isolated respectively. The five Streptococcus suis strains were sequenced by multisite sequencing by measuring the partial fragments of seven housekeeping genes dpr, thrA, cpn60, recA, gki, aroA and mutS on the genome of Streptococcus suis. Through the comparison of the above sequences, we found that the 6 strains of dpr, cpn60, recA, gki, aroA and mutS were identical in all 5 strains. There were two alleles thrA-c and thrA in the thrA gene fragment thrA-h, a neutral mutation (TTA → TTG) occurred in the third position of leucine codon 360 in the allele. MLST analysis showed that isolates of clinical isolates of Streptococcus suis L-SS002, L-SS003 and L-SS005 from Guangdong Province belonged to ST7 type, which was similar to the Sichuan epidemic strain. However, L-SS004 and L-SS006 were not found in Hong Kong The same strain of Streptococcus suis belongs to the ST1 clone, but these five strains are closely related and belong to the ST1 clone complex, which is significantly different from the outbreak of the human swine herd in Sichuan Province, where the latter is only composed of a single ST7 swine chain Coccus caused by cloning. Strain belonging to ST7 is likely to originate from Sichuan; however, the origin of the other two strains of ST1 clone has yet to be identified.