Genomic Diversity and Virulence Profiles of Historical Escherichia coli O157 Strains Isolated from Clinical and Environmental Sources

Abstract

c Escherichia coli O157:H7 is, to date, the major E. coli serotype causing food-borne human disease worldwide. Strains of O157 with other H antigens also have been recovered. We analyzed a collection of historic O157 strains (n ‫؍‬ 400) isolated in the late 1980s to early 1990s in the United States. Strains were predominantly serotype O157:H7 (55%), and various O157:non-H7 (41%) serotypes were not previously reported regarding their pathogenic potential. Although lacking Shiga toxin (stx) and eae genes, serotypes O157:H1, O157:H2, O157:H11, O157:H42, and O157:H43 carried several virulence factors (iha, terD, and hlyA) also found in virulent serotype E. coli O157:H7. Pulsed-field gel electrophoresis (PFGE) showed the O157 serogroup was diverse, with strains with the same H type clustering together closely. Among non-H7 isolates, serotype O157:H43 was highly prevalent (65%) and carried important enterohemorrhagic E. coli (EHEC) virulence markers (iha, terD, hlyA, and espP). Isolates from two particular H types, H2 and H11, among the most commonly found non-O157 EHEC serotypes (O26:H11, O111:H11, O103:H2/ H11, and O45:H2), unexpectedly clustered more closely with O157:H7 than other H types and carried several virulence genes. This suggests an early divergence of the O157 serogroup to clades with different pathogenic potentials. The appearance of important EHEC virulence markers in closely related H types suggests their virulence potential and suggests further monitoring of those serotypes not implicated in severe illness thus far.

Evaluation of clonal relatedness among different sources of E. coli isolates in Iranian children with urinary tract infection (UTI) and age-matched healthy people.

“…The mechanisms underlying the evolution and emergence of such new bacterial pathogens are not well understood, and these atypical strains now are attracting more attention. The variety of virulence determinants due to horizontal gene transfers of mobile elements, such as pathogenicity islands (PAIs), phages and plasmids contributing to a strain's pathogenic potential [6][7][8][9][10].…”

Cytolethal distending toxin producing Escherichia coli O157:H43 strain T22 represents a novel evolutionary lineage within the O157 serogroup

“…Interestingly, T22 also shows the non-sorbitol-fermenting (NSF) phenotype (Tóth et al, 2009). In a more recent study, conducted with 400 O157 strains including nine of the O157:H43 strains, pulsed field gel electrophoresis (PFGE) patterns suggested that the O157 serogroup became divergent according to the different H types (Rump et al, 2015). Out of the nine O157:H43 strains investigated by Rump et al, (2015) only two were NSF, and one of theme lacked all EHECspecific marker genes.…”

“…Similarly, none of the 13 EHEC-specific marker genes are present in the genome of T22. Because the study was limited to these 13 genes, no further genetic comparison is possible at present between T22 and the O157:H43 strains investigated by Rump et al (2015).…”

Genome Sequences of 64 Non-O157:H7 Shiga Toxin-Producing Escherichia coli Strains

“…In 1982, the first Shiga toxin-producing Escherichia coli (STEC) serotype, E. coli O157:H7, was associated with mild to severe human disease and outbreaks ( 1 ). Since then, its diversity has been widely studied ( 2 ). However, not only O157:H7 has been implicated with human diseases, as >400 STEC serotypes have also been found to be responsible for them ( 3 ).…”