Cloning and Sequencing of vt2 A and B Subunit of Bacteriophage Isolated from E.coli O157：H7

According to the nucleotide sequences of the vt1 and vt2 toxin genes in GenBank, four pair of primers were designed and synthesized. vt1 and vt2 were detected in E.coli O157:H7 strains. Bacteriophage was induced and released from the strain only carrying vt2. Phage DNA was extracted and used as PCR template for the detection of the vt2, vt2-A and vt2-B genes. The purified vt2-A and vt2-B fragments were inserted into pMD18-T vector. Sequencing proved that two sequences were genes of subunit A and B of vt2. The homologies of two sequences compared to their corresponding sequences coding VT2 toxin in GenBank (accession numbers X07865, NC_002655, BA000007, AF291819) were 98%~99%, 96%~100%,respectively. Our results revealed that vt2 gene was encoded by bacteriophage, which provides a foundation for further research on horizontal transmission of VT phage carrying virulent gene.