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 toxinproducing 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 (A255T) polymorphism, Shiga toxin-encoding bacteriophage insertion site analysis and variant analysis of Shiga toxin 2 gene (stx2a and stx2c) and antiterminator Q genes (Q933 and Q21). 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 (255T) polymorphism occurred more frequently among human strains than food strains. Q21 and Q933+Q21 were found at significantly higher frequencies among food and human strains, respectively. Moreover, stx2a and stx2a+c were detected at significantly higher frequencies among human strains compared to food strains. Bivariate analysis revealed significant concordance (P<0.05) between the LSPA-6 assay and the other typing methods. Multivariable regression.