Purpose: Identification of genetic differences between stx2-encoding phage may help improve DNA sequence-based subtyping approaches for identifying transmission routes of E. coli O157:H7 during outbreaks.
Methods: The stx2-encoding phage from twenty clinical isolates, including the prototypical strains EDL933 and Sakai were isolated after ciprofloxacin induction and sequenced by 454 technology.
Results: Comparison of phage sequences identified most sequence variation in genes annotated previously as the encoding cII and cIII protein, exonuclease, recombination protein Bet, host-nuclease inhibition protein Gam, Kil, replication protein O, antirepressor, DNA binding protein, antiterminator Q and C4 Zn-finger protein. Moreover, we observed that the presence and position of an insertion sequence (IS629) element varied. Additionally, the sequenced phages were more similar to Sp5 from strain Sakai than the stx2-encoding phage from EDL933. We also observed differences in the expression of Stx2between strains.
Significance: The regions identified in this study might be useful as markers to increase the discriminatory power of multilocus sequence typing protocols for E. coli O157:H7 and sequence analysis may provide insights into the responsible mechanism(s).