Sequence diversity of the Escherichia coli H7 fliC genes: implication for a DNA-based typing scheme for E. coli O157:H7.

Flagellar (H) antigens are mostly encoded by genes at the fliC locus in E. coli. We have sequenced 11 H7 fliC genes from Escherichia coli strains that belong to seven O serotypes. These sequences, together with those of nine other H7 fliC genes (from strains of three different O serotypes) sequenced recently (S. D. Reid, R. K. Selander, and T. S. Whittam, J. Bacteriol. 181:153-160, 1999), include 10 different sequences. The differences between these 10 sequences range from 0.06 to 3.12%. By comparison with other E. coli flagellin genes, we have identified primer length sequences specific for H7 genes in general and others specific for H7 genes of O157 and O55 strains: the specificity was confirmed by PCR testing the type strains for all 53 E. coli H types. We have previously identified genes specific for the E. coli O157 antigen, and use of the combination of O157- and H7-specific primers allows the sensitive and rapid detection of O157:H7 E. coli strains, which cause the majority of hemorrhagic colitis cases.