(A) Field inversion gel electrophoresis of LA-PCR products obtained from 6 control strains and 24 representative strains differentiated by the PCR-RFLP assay. Lanes: 1 and 32, 5-kb DNA ladder; 2, C600; 3, C600 (Stx1φ); 4, C600 (Stx2φ-I); 5, C600 (Stx2φ-II); 6, C600 (933W phage); 7, RIMD0509952 (Sakai strain; VT1-Sakai phage, VT2-Sakai phage); 8, 1-A (Okayama, Japan); 9, 2-B (Osaka, Japan); 10, 3-C (Okayama, Japan); 11, 4-D (Okayama, Japan); 12, 5-E (Okayama, Japan); 13, 6-F(Okayama, Japan); 14, 7-G (Osaka, Japan); 15, 8-H (Osaka, Japan); 16, 9-I (Osaka, Japan); 17, 10-J (Osaka, Japan); 18, 11-K (Nagano, Japan); 19, 12-L (Nagano, Japan); 20, 13-M (Nagano, Japan); 21, 14-N (Nagano, Japan); 22, 15-O (Nagano, Japan); 23, 16-P (United States); 24, 17-Q (United States); 25, 18-R (United States); 26, 19-S (United States); 27, 20-T (United States); 28, 21-U (Canada); 29, 22-V (Canada); 30, 23-W (Canada); 31, 24-X (Canada). Field inversion gel electrophoresis of BglI digest (B) and EcoRV digest (C) of LA-PCR products obtained from 6 control strains and 24 representative strains differentiated by the PCR-RFLP assay. Lanes: 1, λ-HindIII digest; 2, 32, 1-kb DNA ladder; 3, C600 (Stx1φ); 4, C600 (Stx2φ-I); 5, C600 (Stx2φ-II); 6, C600 (933W phage); 7, RIMD0509952 (Sakai strain; VT1-Sakai phage, VT2-Sakai phage); 8, 1-A (Okayama, Japan); 9, 2-B (Osaka, Japan); 10, 3-C (Okayama, Japan); 11, 4-D (Okayama, Japan); 12, 5-E (Okayama, Japan); 13, 6-F (Okayama, Japan); 14, 7-G (Osaka, Japan); 15, 8-H (Osaka, Japan); 16, 9-I (Osaka, Japan); 17, 10-J (Osaka, Japan); 18, 11-K (Nagano, Japan); 19, 12-L (Nagano, Japan); 20, 13-M (Nagano, Japan); 21, 14-N (Nagano, Japan); 22, 15-O (Nagano, Japan); 23, 16-P (United States); 24, 17-Q (United States); 25, 18-R (United States); 26, 19-S (United States); 27, 20-T (United States); 28, 21-U (Canada); 29, 22-V (Canada); 30, 23-W (Canada); 31, 24-X (Canada).