Characterization of Escherichia coli O157：H7 isolated in China by multiple-locus variable number of tandem repeat analysis

Objective To type the enterohemorrhagic Escherichi coli(E.coli)O157:H7 strains isolated in China by multiple-locus variable number of tandem repeat analysis(MLVA). Methods Seven variable number of tandem repeat (VNTR)loci were chosen.E.coli isolates were typed by PCR and capillary electrophoresis.A dendrogram was constructed by BioNumeries. Results The 135 strains of E.coli O157:H7 isolated in China from 1999 to 2002 were classified into three clusters(A,B,C)and 38 MLVA types.The percentages of cluster A,B,and C were 20.7%(28/135),23.7%(32/135),and 55.6%(75/135),respectively.The strains isolated in the same area shared a common MLVA type and the strains from an outbreak exhibited the same MLVA type. Conclusion The strains of E.coli O157:H7 isolated in China are genetic polymorphic.MLVA has a higher discriminative typing power and could contribute to better understanding of E.coli O157:H7 infection in epidemiologic investigation.