Molecular characterization and clonal analysis of strains of Escherichia coli O157 group isolated from different sources

Fourteen, O157 serogroup Escherichia coli strains, isolated from humans, cattle, and pigs in Poland and in Germany, were investigated by means of molecular biological methods. The presence of genes encoding the production of H7 flagellar antigen, Shiga toxins, intimin (including all five of its variants), translocated intimin receptor, and enterohemolysin, was investigated by PCR. It was demonstrated that only 3 strains had the H7 genes; therefore, they were classified as O157:H7. The Shiga toxin markers were detected in all 10 but one strains isolated from humans and from cattle, whereas none of the four O157 isolates of pig origin was stx-positive. The eaeA intimin (all-gamma variant) and ehly enterohemolysin genes were found in 10 and in 11 strains, respectively, whereas the tir marker was detected in 7 isolates. The genetic relatedness of the strains was examined by the amplification of DNA sequences located between the repetitive element IS3 by the IS-PCR method. The electrophoretic picture of the amplicons obtained was analysed by the UPGMA test with the Jaccard coefficient, and it was demonstrated that the E. coli strains tested were classified into 4 distinct clonal lineages. A close-genetic correlation between bacteria isolated in Poland and in Germany was also observed. The results obtained showed that IS-PCR is a powerful tool for revealing the clonal nature and genetic differences among E. coli O157 strains isolated from different sources.