Abstract
Among Shiga toxin (Stx)–producing Escherichia coli (STEC) O157:H7 strains, those producing Stx2a cause more severe diseases. Atypical STEC O157:H7 strains showing a β-glucuronidase–positive phenotype (GP STEC O157:H7) have rarely been isolated from humans, mostly from persons with asymptomatic or mild infections; Stx2a-producing strains have not been reported. We isolated, from a patient with bloody diarrhea, a GP STEC O157:H7 strain (PV15-279) that produces Stx2a in addition to Stx1a and Stx2c. Genomic comparison with other STEC O157 strains revealed that PV15-279 recently emerged from the stx1a/stx2c-positive GP STEC O157:H7 clone circulating in Japan. Major virulence genes are shared between typical (β-glucuronidase–negative) and GP STEC O157:H7 strains, and the Stx2-producing ability of PV15-279 is comparable to that of typical STEC O157:H7 strains; therefore, PV15-279 presents a virulence potential similar to that of typical STEC O157:H7. This study reveals the importance of GP O157:H7 as a source of highly pathogenic STEC clones.
Highlights
Among Shiga toxin (Stx)–producing Escherichia coli (STEC) O157:H7 strains, those producing Stx2a cause more severe diseases
The results clearly indicate that PV15-279 formed a distinct cluster with all other GP STEC O157:H7 strains, including 2 US isolates, and is a strain that recently emerged from the stx1a/stx2c-positive clone circulating in Japan
The whole-genome sequence-based phylogenetic analysis, which included additional GP STEC O157:H7 strains and representative strains belonging to other E. coli O55/O157 lineages, revealed that PV15-279 recently emerged by the acquisition of Stx2a phage from the stx1a/ stx2c-positive GP STEC O157:H7 clone circulating in Japan (Figure 2)
Summary
Among Shiga toxin (Stx)–producing Escherichia coli (STEC) O157:H7 strains, those producing Stx2a cause more severe diseases. Atypical STEC O157:H7 strains showing a β-glucuronidase–positive phenotype (GP STEC O157:H7) have rarely been isolated from humans, mostly from persons with asymptomatic or mild infections; Stx2aproducing strains have not been reported. SF STEC O157:H– strains are usually stx2a positive [10]; like typical STEC O157:H7, they have caused many outbreaks and sporadic cases of hemolytic uremic syndrome in Germany and other countries in Europe. This clone is generally thought to be highly pathogenic [11,12,13]. The virulence potential of GP STEC O157:H7 remains to be fully elucidated
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