Genetic diversity of Shiga toxin-producing Escherichia coli O157: H7 recovered from human and food sources

The aim of this study was to identify an epidemiological association between Shiga toxin-producing Escherichia coli O157 : H7 strains associated with human infection and with food sources. Frequency distributions of different genetic markers of E. coli O157 : H7 strains recovered from human and food sources were compared using molecular assays to identify E. coli O157 : H7 genotypes associated with variation in pathogenic potential and host specificity. Genotypic characterization included: lineage-specific polymorphism assay (LSPA-6), clade typing, tir (A2557) polymorphism, Shiga toxin-encoding bacteriophage insertion site analysis and variant analysis of Shiga toxin 2 gene (stx(2a) and stx(2c)) and antiterminator Q genes (Q(933) and Q(21)). The intermediate lineage (LI/II) dominated among both food and human strains. Compared to other clades, clades 7 and 8 were more frequent among food and human strains, respectively. The tir (2557) polymorphism occurred more frequently among human strains than food strains. Q(2)1 and Q(933+Q21) were found at significantly higher frequencies among food and human strains, respectively. Moreover, stx(2a) and stx(2a+c) were detected at significantly higher frequencies among human strains compared to food strains. Bivariate analysis revealed significant concordance (P