Study on evolution of pO157 in E. coli O157:H7 strains isolated in China

Objective To investigate the evolution of pO157 of O157:H7 strains isolated in China. Methods The classification of the strains was conducted by using restriction enzyme digestion, the amplification by using overlapping primer PCR amplification and the confirmation by using Southern blot. Finally the sequencing was done. Results Sixty strains of E. coli O157:H7 were classified as 5 groups(A-E) by enzyme digestion. However A group and C group were actually belonged to one group because the enzyme digestion difference was caused by a small plasmid in C group using HindⅢ digestion. PCR products from primer pairs 5 and 25 differed between A, C groups and pO157. Only PCR fragments from primer pair 25 showed difference between B group and pO157. The reason for the PCR fragment difference from pair 25 between A-C groups and pO157 was the introduction of IS1310. Conclusion pO157 in the isolated O157:H7 strains in China is relatively conserved. The evolution of pO157 in the O157:H7 strains isolated in China was mainly caused by some inserted sequences such as IS1310.