Subtyping method for Escherichia coli shiga toxin (verocytotoxin) 2 variants and correlations to clinical manifestations

Abstract

Shiga toxin 2 (Stx2) from Shiga toxin-producing Escherichia coli (STEC) was subtyped by a method involving partial sequencing of the stxAB2 operon. Of 255 strains from the Danish STEC cohort, all 20 cases of hemolytic-uremic syndrome were associated with subtype Stx2 (11 cases), subtype Stx2c (1 case), or the two combined (8 cases).

FIG. 1.

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.

FIG. 2.

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 and , respectively. The same clustering was observed when the entire sequence of 408 joined A- and B-subunit stx₂ holotoxin sequences in GenBank was analyzed.