Characterization of Shiga toxin-producing Escherichia coli isolated from aquatic environments

This study reports the phenotypic and genotypic characterization of 144 Shiga toxin-producing Escherichia coli (STEC) strains isolated from urban sewage and animal wastewaters using a Shiga toxin 2 gene variant (stx2)-specific DNA colony hybridization method. All the strains were classified as E. coli and belonged to 34 different serotypes, some of which had not been previously reported to carry the stx2 genes (O8:H31, O89:H19, O166:H21 and O181:H20). Five stx2 subtypes (stx2, stx2c, stx2d, stx2e and stx2g) were detected. The stx2, stx2c, stx2d and stx2e subtypes were present in urban sewage and stx2e was the only stx2 subtype found in pig wastewater samples. The stx2c and stx2g were more associated with cattle wastewater. One strain was positive for the intimin gene (eae) and five strains of serotypes were positive for the adhesin encoded by the saa gene. A total of 41 different seropathotypes were found. On the basis of occurrence of virulence genes, most non-O157 STEC strains are assumed to be low-virulence serotypes.