FIG. 1.

(A) Southern blot analysis of the agarose gel of first-round PCR products hybridized with the Stx 2-radiolabeled probe (35). (B) Agarose gel electrophoresis and ethidium bromide staining of nested PCR products, with the first-round PCR products as templates. Lanes: 1, DNA from E. coli ATCC 43889, which bears Stx 2; 2, DNA from bacteriophage 933W, which bears Stx 2 (23); 4, 8, and 12, DNA of bacteriophages purified from 10 ml of sewage; 5, 9, and 13, DNA of bacteriophages purified from 1 ml of sewage water; 3, 6, and 10, DNA from E. coli ATCC 43888, which does not bear Stx 2; 7, 11, and 14, negative controls containing no template; M, molecular weight marker, φX-174-RF DNA HaeIII digest.