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Multilocus sequence typing (MLST) of EHEC and aEPEC strains of the four most important non-O157 Serotypes (O26, O103, O111, O145) revealed that these strains represent a single sequence type complex (STC) - STC29. Within ST16, ST21, ST29 and ST113, the major sequence types of STC29, the mentioned serotypes cluster together. Furthermore both, aEPEC and EHEC, can be designated to the same STs. Hence STC29 displays the close relationship between aEPEC and EHEC and their connected evolutionary background, even though they were characterized as different serotypes by now.
For this reason we have chosen 100 strains of STC29 for whole genome sequencing. The strains were isolated from human patients (n=54) and cattle (n=64), and belong to both pathotypes aEPEC and EHEC. The maximum common genome (MCG) of the 100 genomes was defined by identifying a set of conserved genes occurring in every of the considered genomes. The following single nucleotide polymorphisms (SNP) analysis of 3.710 orthologous genes revealed >30.000 SNP-sites. On the basis of these SNPs maximum spanning trees (MSTs) were generated to highlight the different characteristics of each strain (ST, pathotype and host).
Clusters formed within the SNP-site based MST represented the single seuqnece types of an allele based MST. This underlines that the MLST of seven housekeeping genes is a powerful method to display the relationship of E. coli strains. For the representation of the pathotype within this MST no tendency was recognizable, underlining the similarity between EHEC and aEPEC strains and their likely equal evolutionary background. For the host the strains originated from no cluster formation was revealed, which rejects a host specificity of the strains and therefore supports the evidence for zoonotic transmission of EHEC and aEPEC strains.