Use of representational difference analysis to identify Escherichia coli O157-specific DNA sequences.

Whereas several important virulence factors in Escherichia coli O157 have been identified, studies suggest they are not always essential and are probably insufficient to account for the severe clinical manifestation of E. coli O157 infection. Identification of putative virulence determinants is crucial to the understanding of bacterial pathogenesis and genomic comparison analysis may aid the characterisation of unidentified virulence attributes. In this study, representational difference analysis (RDA) was used for genomic comparison of E. coli O157 with the proposed ancestral strain, E. coli O55. Unique E. coli O157 gene sequences were isolated and one, termed RDA-1, taken forward for further analysis. Southern blotting with labelled RDA-1 as a probe showed it to be present in 77% of E. coli O157 isolates and absent in all non-E. coli O157 screened. Sequence flanking RDA-1 was obtained from a genomic clone identified by hybridisation, and contained an open reading frame predicted to encode a novel iron-regulated outer membrane protein.