Shiga toxin-producing Escherichia coli (STEC) arise after the insertion of a group of bacteriophages encoding the Stx gene. Shiga toxin-producing bacteriophages (Stx phages), notably, are heterogeneous with mosaic genomic structures. However, little is known of the genetic diversity of Stx phages across STEC populations. Here, we examined the diversity of Stx prophages among E. coli isolated from 52 animals from 4 Michigan cattle herds between 2011 and 2012 using a novel long range PCR-based restriction fragment length polymorphism (RFLP) method that targets a distinct region (ciii-stx, 10-17 kb) within three Stx phage subtypes. Sixteen Stx phage types (PT) were identified; 10 of the 16 Stx PT encoded Stx1, while three encoded Stx2a and another three encoded Stx2c. Interestingly, the same Stx PT was frequently identified within each cattle herd; despite the STEC genotypes are diverse in the herd. These data suggest that transmission of both STEC and Stx phages occurs regularly and provides insight into the diversity and dynamics of specific Stx phages within and across herds. Identifying the distribution of Stx PT present in the cattle reservoir would enable the linkage to STEC epidemiology study, and to further determine whether specific Stx PT contribute to higher virulence in STEC infection.
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