Characterization of Shiga toxin-producing Escherichia coli isolates associated with two multistate food-borne outbreaks that occurred in 2006.

Shiga toxin-producing Escherichia coli isolates from two 2006 outbreaks were compared to other O157:H7 isolates for virulence genotype, biofilm formation, and stress responses. Spinach- and lettuce-related-outbreak strains had similar pulsed-field gel electrophoresis patterns, and all carried both stx2 and stx2c variant genes. Cooperative biofilm formation involving an E. coli O157:H7 strain and a non-O157:H7 strain was also demonstrated.