FIG. 2.

PCR detection of the H7 fliC variant in phylogenetically diverse E. coli lineages. Thirty-five H7-positive control isolates from various H7-associated clonal groups were uniformly positive for the 547-bp H7 fliC PCR product (lanes 2 to 5), whereas 45 negative-control strains representing 35 other H types were uniformly negative (lanes 7 to 10). Among 75 unknown strains (lanes 12 to 17), all representatives of the O1:K1:H- clonal group were H7 fliC positive (lane 12), whereas all O7:K1:H- strains were H7 fliC negative (lane 13). Most strains of uncertain H status that were suspected of being members of the O18:K1:H7 clonal group were H7 fliC positive, whether they had been typed as having another H antigen (lane 14), as having multiple H antigens (lane 15), or as being H untypeable (lane 16) or were nonmotile (lane 17). Similar results were obtained for unknown strains putatively representing the O1:K1:H7 or O2:K1:H7 clonal groups (not shown). M, 100-bp molecular weight ladder (lanes 1 and 18).