Abstract
Highly pathogenic enterohemorrhagic Escherichia coli (EHEC) O157 cause a spectrum of clinical signs that include diarrhea, bloody diarrhea, and hemolytic uremic syndrome. The current evolutionary model of EHEC O157:H7/H(-) consists of a stepwise evolution scenario proceeding from O55:H7 to a node (hypothetical intermediate) that then branches into sorbitol-fermenting (SF) O157:H(-) and non-SF (NSF) O157:H7. To identify this hypothetical intermediate, we performed single nucleotide polymorphism analysis by sequencing of 92 randomly distributed backbone genomic regions of 40 O157:H7/H(-) isolates. Overall, 111 single nucleotide polymorphisms were identified in 75/92 partial open reading frames after sequencing 51,041 nt/strain. The EHEC O157:H7 strain LSU-61 from deer occupied an intermediate position between O55:H7 and both O157 branches (SF and NSF O157), complementing the stepwise evolutionary model of EHEC O157:H7/H(-). The animal origin of this intermediate emphasizes the value of nonhuman reservoirs in the clarification of the evolution of human pathogens.
Highlights
Pathogenic enterohemorrhagic Escherichia coli (EHEC) O157 cause a spectrum of clinical signs that include diarrhea, bloody diarrhea, and hemolytic uremic syndrome
The E. coli O157:H– strain LSU-61, which was isolated from a deer [10,13], had been previously discussed by Feng et al as a potential intermediate, but that hypothesis was rejected because the strain lacked a gene encoding Shiga toxin and had a distinct multilocus sequence typing (MLST) sequence type [10]
Further characterization by MLST of prototype strains that defined subgroups and clusters resulted in identical STs for all SF and NSF O157 (ST11) and in closely related STs of the O55:H7 strains (ST335)
Summary
Pathogenic enterohemorrhagic Escherichia coli (EHEC) O157 cause a spectrum of clinical signs that include diarrhea, bloody diarrhea, and hemolytic uremic syndrome. The current evolutionary model of EHEC O157:H7/H– consists of a stepwise evolution scenario proceeding from O55:H7 to a node (hypothetical intermediate) that branches into sorbitol-fermenting (SF) O157:H– and non-SF (NSF) O157:H7. To identify this hypothetical intermediate, we performed single nucleotide polymorphism analysis by sequencing of 92 randomly distributed backbone genomic regions of 40 O157:H7/H– isolates. We used an SNP-based approach to examine isolates from different sources of EHEC O157:H7/H– to further elucidate the evolutionary model of emergence of this pathogen, paying particular attention to identifying the “missing link” hypothetical intermediate
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