FIG. 4.

Electrophoresis for 55 (A) and 75 (B) min. Comparison of the eight KSU strains that gave discrepant results with the RSS-PCR and serological tests. Lane 1 represents the 1-kb DNA ladder (Gibco-BRL). Lane 2 represents the E. coli O157:H7 pattern A (positive control). Lanes 3 to 8 represent non-O157:H7 strains with pattern H (KSU strains 14, 41, 43, 45, 46, and 48). Lane 9 represents a non-O157:H7 strain with pattern E (KSU strain 49). Lane 10 represents KSU strain 52 which was found to be missing the H7 antigen but which still gave a pattern similar to that of E. coli O157:H7 pattern A. A longer separation time yielded better discrimination of the patterns.