Our findings indicate that about half of the typical and atypical EPEC strains and serotypes are closely related to EHEC regarding these virulence attributes (Table 2). The presence of OI-122 encoded genes, followed by OI-71 were most significant for the assignment of EPEC to the “”EHEC-related”" Cluster 1 confirming data from our previous study performed on a different collection of strains [17]. The OI-57 encoded

genes nleG5-2 and nleG6-2, as well as the espK gene were not as strongly associated with Cluster 1, as the OI-122 and OI-71 genes. Recently, the OI-57 associated genes adfO and ckf were reported to be present in 30 (71%) of 42 investigated EPEC strains GW3965 purchase but a high variability of OI-57 associated orfs in EPEC strains was observed [28]. This could explain the results of our study, where the OI-57 associated nleG5-2 gene was found check details infrequently in all EPEC, whereas the nleG6-2 gene was frequent in atypical EPEC (45.5%) but rarely found in typical EPEC (12.3%) (Table 1). Further work is needed to define the genes of OI-57 that are most suitable for the molecular risk assessment of EHEC and EPEC strains. In our study, EHEC-plasmids were associated with EHEC, STEC and Ro 61-8048 mw atypical EPEC, but not with typical EPEC strains. EHEC-plasmids are frequently harboured by classical EHEC

but also by many LEE-negative Exoribonuclease STEC strains [32–34]. Correspondingly, EHEC-plasmid encoded genes ehxA, etpD, katP and espP had only a small influence on Cluster 1 formation, confirming results of previous studies [16, 17]. In this study, EHEC-plasmid genes were significantly more associated with atypical EPEC Cluster 1 than with Cluster 2 strains. The high proportion of EHEC-plasmid

positives among Cluster 1 strains suggests that many of these may have derived from EHEC by losing stx-genes. A loss of stx-genes was reported to occur frequently in classical EHEC strains [23, 26]. EHEC-plasmid genes were found in 23/29 (79.3%) of atypical EPEC Cluster 1 strains belonging to EHEC related serotypes O26:H11, O103:H2, O145:H28 and O157:H7 (data not shown). These 30 EHEC-like strains showed the same virulence characteristics (presence of OI-122 genes) as their homologous EHEC strains. In addition to this, there are epidemiological findings pointing to a closer relationship between “”Cluster 1″” atypical EPEC and EHEC strains. Significantly (p < 0.05) more typable (78/120 = 65.0%) Cluster 1 strains than Cluster 2 strains belonged to serotypes (18/40 = 45.0%) that are associated with the production of Shiga toxins (38). Only 26.6% (24/90) of the atypical EPEC strains of Cluster 2 showed O:H types (10/46 = 21.7) previously associated with Stx-production. Typical EPEC were also found to split into Cluster 1 and Cluster 2 strains.