Sorbitol-Fermenting Enterohemorrhagic Escherichia coli O157:H Isolates from Czech Patients with Novel Plasmid Composition Not Previously Seen in German Isolates.

Sorbitol-fermenting (SF) enterohemorrhagic (EHEC) O157:H strains, first identified in Germany, have emerged as important pathogens throughout Europe. Besides chromosomally encoded Shiga toxin 2a (the major virulence factor), several putative virulence loci, including the , , and operons, encoding EHEC hemolysin, type II secretion system proteins, and Sfp fimbriae, respectively, are located on the 121-kb plasmid pSFO157 in German strains. Here we report novel SF EHEC O157:H strains isolated from patients in the Czech Republic. These strains share the core genomes and chromosomal virulence loci encoding toxins ( and the -ABC operon) and adhesins (-γ, , , and ) with German strains but differ essentially in their plasmids. In contrast to all previously detected SF EHEC O157:H strains, the Czech strains carry two plasmids, of 79 kb and 86 kb. The 79-kb plasmid harbors the operon, but neither of the plasmids contains the and operons. Sequence analyses demonstrated that the 79-kb plasmid (pSFO157 258/98-1) evolved from pSFO157 of German strains by deletion of a 41,534-bp region via homologous recombination, resulting in loss of the and operons. The 86-kb plasmid (pSFO157 258/98-2) displays 98% sequence similarity to a 92.7-kb plasmid of an extraintestinal pathogenic bloodstream isolate. Our finding of this novel plasmid composition in SF EHEC O157:H strains extends the evolutionary history of EHEC O157 plasmids. Moreover, the unique molecular plasmid characteristics permit the identification of such strains, thereby facilitating further investigations of their geographic distribution, clinical significance, and epidemiology. Since their first identification in Germany in 1989, sorbitol-fermenting enterohemorrhagic O157:H (nonmotile) strains have emerged as important causes of the life-threatening disease hemolytic-uremic syndrome in Europe. They account for 10 to 20% of sporadic cases of this disease and have caused several large outbreaks. The strains isolated throughout Europe share conserved chromosomal and plasmid characteristics. Here we identified novel sorbitol-fermenting enterohemorrhagic O157:H patient isolates in the Czech Republic which differ from all such strains reported previously by their unique plasmid characteristics, including plasmid number, composition of plasmid-carried virulence genes, and plasmid origins. Our findings contribute substantially to understanding the evolution of O157 strains and their plasmids. In practical terms, they enable the identification of strains with these novel plasmid characteristics in patient stool samples and thus the investigation of their roles as human pathogens in other geographic areas.