A total of 255 STEC strains were subjected to partial sequencing of the stxAB₂ operon, and the coding regions were translated. The figure shows an alignment (ClustalW) of the resulting 159 amino acids (95 amino acids of the C-terminal part of subunit A [positions 225 to 319] and 64 amino acids of the N-terminal part of subunit B [positions 1 to 64]). The toxin variants are named by subtype, O group, and strain name. With respect to the 159 residues, the sequences for the following toxin variants are registered under the respective GenBank accession numbers: Stx2-O48-94C, Z37725; Stx2-O157-EDL933, X07865; Stx2c-O157-C394-03, DQ235774; Stx2c-O157-FLY16, AB015057; Stx2d-O73-C165-02, DQ059012; Stx2d-O8-C466-01B, DQ235775; Stx2d3-O157-7279, X61283; Stx2e-O101-E-D43, X81417; Stx2e-ONT-26725-97, AJ567998; Stx2g-Out-S-8, AB048227; Stx2c-O111-PH, L11078; Stx2c-O118-EH250, AF043627.

Phylogenetic tree (unweighted-pair group method using average linkages) based on the alignment shown in Fig. 1 of the 159 amino acids partially covering the stxAB₂ operon of the 12 toxin variants from this study. Roman numbers (I, II, III, and IV) and capital letters (B1, B2, and C) refer to previous groupings introduced in references 1 and 2, respectively. The same clustering was observed when the entire sequence of 408 joined A- and B-subunit stx₂ holotoxin sequences in GenBank was analyzed.