Agarose gel electrophoresis (A) and hybridization with the cdtB probe (B) of EcoRV-digested genomic DNA from cdt-harboring STEC strains and controls. Lanes S, molecular mass markers (digoxigenin-labeled DNA Molecular Weight Marker II; Roche Biochemicals). In lanes 1 to 8, the following STEC strains (serotypes and cdt alleles are shown in parentheses) are displayed: lane 1, strain 9282/01 (serotype O91:H21, allele cdt-V); lane 2, 2596/02 (O91:H21, cdt-V); lane 3, 5249/01 (O113:H21, cdt-V); lane 4, 2896/01 (O113:H21, cdt-V); lane 5, 2996/96 (O73:H18, cdt-V); lane 6, 9063/02 (O153:H18, cdt-III); lane 7, 7272/02 (O153:H18, cdt-III); lane 8, 5107/00 (O153:H18, cdt-III). Lanes 9 to 11 contain control strains as follows: lane 9, strain 493/89 (SF STEC serotype O157:H−, allele cdt-V); lane 10, 1404 (NTEC O78:H?, cdt-III); lane 11, E. coli C600 (negative control). Arrows in panel A indicate the EcoRV fragments that hybridized with the cdtB probe.