Abstract
One hundred twenty-four Escherichia coli O157:H7 isolates were characterized by pulse-field gel electrophoresis, bacteriophage typing, and PCR of verotoxin genes. Diversity indices obtained--0.786 for phage types and 0.987 for pulsed-field gel electrophoresis types--demonstrated that phage typing falls below the critical value (0.9) required for confident interpretation of results.