大肠埃希菌O157∶H7携带stx2::IS1203v基因研究

目的了解中国部分地区大肠埃希菌O157：H7菌株携带志贺毒素基因变异状况。方法采用聚合酶链反应扩增志贺毒素基因，使用核苷酸序列测定判断是否存在志贺毒素的新变种，用HeLa细胞毒性实验研究其细胞毒性的变化。结果1992—2002年中国部分地区分离到的289株产志贺毒素的大肠埃希菌O157：H7中有3株菌携带的志贺毒素2（stx2）基因有1．3kb的插入序列（IS）插入，且这段IS和IS1203变种（IS1203 variant，IS1203v）有100％的核苷酸序列同源性。IS1203v插入到3株大肠埃希菌O157：H7 stx2基因的位置及开放性读码框（ORF）方向有所不同。除此之外，3株菌原有的stx2基因序列完全一致且为Stx2原型毒素。和Stx2原型毒素相比，这3株携带stx2：：IS1203v基因的菌株对HeLa细胞的毒性明显降低。结论分离到IS1203v插入stx2基因的大肠埃希菌O157：H7菌株；IS1203v的插入可导致对HeLa细胞的细胞毒性降低。

Identification of harboring stx2:: IS1203 Escherichia coli O157:H7 strains isolated in China

OBJECTIVE: To understand the variation of Shiga toxin (stx) genes of Escherichia coli O157:H7 strains isolated in China. METHODS: Polymerase chain reaction (PCR) was used to identity the types of stx genes and the nucleotide sequences of the amplified stex variants genes were determined. Compare to the cytotoxicity of Stx,variants were tested by HeLa cell assay. RESULTS: We found novel stx2 genes in 3 of 289 strains of Shiga toxin-producing E. coli O157:H7 isolated from 1999 to 2002 in China. The novel stx2 genes were inserted by a 1.3-kb insertion sequence (IS) and the nucleotide sequences of IS showed 100% homology with that of IS1203 variant (IS1203v). The IS1203v inserted in the stx2 genes of three E. coli O157:H7 strains at different sites and the direction of the open reading frames (ORFs) of IS1203v of each strain was different. In addition to the above mentioned findings, the nucleotide sequences of three stx2 genes were completely identical and the type of the three Stx2 was Stx2 prototype. Compare to the cytotoxicity of Stx2 prototype, the novel Stx2 was found to be obviously lower. CONCLUSION: E. coli O157:H7 strains harboring stx2::IS1203v genes were isolated in China. Consequently, the results of HeLa cell assay showed that the insertion of IS1203v could lead to low cytotoxicity of Stx2.