PFGE patterns of XbaI-digested fragments obtained when wild-type and successive-passage-derived STEC strains RIMD0509952 (A), EC1015 (B), and 83-1385 (C). (A) PFGE profiles obtained with STEC O157:H7 strain RIMD0509952 and its passage-derived strains. Lanes: 1, I-a (original pattern); 2, I-b; 3, I-c; 4, I-d; 5, I-e; 6, I-f. (B) PFGE profiles obtained with STEC O157:H7 strain EC1015 and its passage-derived strains. Lanes: 1, II-a (original pattern); 2, II-b; 3, II-c; 4, II-d; 5, II-e; 6, II-f; 7, II-g; 8, II-h; 9, II-i; 10, II-j; 11, II-k; 12, II-l; 13, II-m; 14, II-n; 15, II-o; 16, II-p; 17, II-q. (C) PFGE profiles obtained with STEC O157:H7 strain 83-1386 and its passage-derived strains. Lanes: 1, III-a (original pattern); 2, III-b; 3, III-c; 4, III-d; 5, III-e; 6, III-f; 7, III-g. Lambda ladders were used as molecular size markers. Positions of DNA fragments with known molecular masses are indicated. Parentheses and asterisks represented additional and lost bands, respectively.