Figure 5. PCR results from representative clinical isolates illustrate that the Shiga toxin 1a gene (stx1a) is phage encoded and inserted into the S1742 locus of Shigella flexneri. PCRs based on the primer scheme detailed in Figure 4 are shown for 6 stx1a-positive strains (BS937, BS938, BS942, BS954, BS974, BS980) and 1 stx1a-negative isolate (BS952). To show that stx1a is phage encoded, we used primer pairs Stx1R2/Phage_stxR2 (A) and Phage_stx1F2.Stx1F2 (B). To analyze the insertion of ϕPOC-J13 into locus S1742, we used primer pairs S1742_up/Stx_phage_up (C) and Stx_phage_dn/S1742_dn (D).