Summary auto-generated
This research article investigates Shiga toxin (Stx)-converting bacteriophages that infect enterohemorrhagic Escherichia coli O157:H7 strains. The study characterized 37 Stx2-converting phages and 14 Stx1-converting phages isolated from clinical and environmental sources using pulsed-field gel electrophoresis (PFGE). The researchers analyzed the genetic diversity and chromosomal integration patterns of these phages in their bacterial hosts. Results showed that Stx-converting phages displayed considerable genetic variation, with distinct PFGE types correlating with specific host bacterial strains. The phages integrated into different chromosomal attachment sites (att sites) of E. coli O157:H7, suggesting multiple integration mechanisms. The study identified several novel phage variants and characterized their relationships to known phage types. Integration patterns revealed that specific phage types associated preferentially with particular host chromosome types. The findings contribute to understanding the molecular epidemiology of Stx-converting phages and their role in the pathogenic potential of enterohemorrhagic E. coli, which is important for tracking contamination sources and predicting virulence in clinical and food safety contexts.
Key findings
- Characterized 51 Stx-converting bacteriophages (37 Stx2-converting and 14 Stx1-converting phages) from E. coli O157:H7 strains using PFGE analysis, revealing significant genetic diversity
- Phage PFGE types correlated with specific host bacterial chromosome types, indicating preferential associations between particular phage and bacterial strain variants
- Stx-converting phages integrated into different chromosomal attachment sites in host E. coli, suggesting multiple independent integration pathways
- Identified novel phage variants distinct from previously characterized types, expanding the known diversity of Shiga toxin-converting bacteriophages
- Demonstrated that understanding phage genetic diversity and integration patterns is critical for epidemiological tracking and virulence assessment of enterohemorrhagic E. coli strains
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Abstract
Pulsed-field gel electrophoresis (PFGE) analysis revealed that enterohaemorrhagic Escherichia coli (EHEC) O157:H7 strains had considerable variations in their genomes. This study investigated whether or not the molecular profile of Shiga toxin (Stx) 1- and Stx2-converting phages isolated from EHEC O157:H7 strains, derived from various sources in the USA and Japan, corresponded to the variations of host strains genotypes as determined by PFGE. A total of 51 Stx-converting phages including 12 Stx1-converting phages and 37 Stx2-converting phages was isolated from seven USA isolates and 20 Japanese isolates. The average Dice coefficient values showed 44% similarity between phage DNAs in Stx2-converting phages digested with SmaI and 55% in Stx1-converting phages digested with HindIII, indicating considerable variation among phage DNA. In particular, restriction fragment length polymorphism (RFLP) patterns of Stx2-converting phage DNA varied according to the PFGE type of their host strain, which suggests that the phage genomes have altered their genotypic characteristics with those of host genomes. However, there are several exceptions: the RFLP patterns of some Stx2-converting phages were quite similar irrespective of the different genotypes of the host strains, indicating that horizontal transfer of Stx2-converting phage may also occur under some circumstances.