A dna fragment of 348 - bp amplified from the b subunit gene was cut into two dna fragment of 216 and 132 - bp by haelli . endonuclease restriction analysis of the plasmid content with psti showed that strainas with the same result of southern - blot with spesific probe had the different cleavage pattern . the isolated 285 - bpand 348 - bp dna was ligated with plasmid puc18 . the ligation mixture was used to transform e . coli jm109and the transformants were plated on lb agar containing antibiotics . plasmid dna containing cloned genes were used for direct sequencing 提示1999年的疫情由不同的病原菌引起。另外使用针对志贺毒素2及其变种的引物对进行pcr检测、细菌染色体pst和pcr产物的hae 、 ras酶切分析，以及pcr产物的序列分析，发现2000年从江苏省徐州市患者和家畜家禽粪便标本分离的大肠杆菌o157 ： h7菌株仅仅携带slt2vha基因。
