Sequence of the Escherichia coli O121 O-antigen gene cluster and detection of enterohemorrhagic E. coli O121 by PCR amplification of the wzx and wzy genes.

The DNA sequence of the 15,155-bp O-antigen gene cluster of Escherichia coli O121 was determined, and 14 open reading frames were identified (all had the same transcriptional direction). Analyses of results indicated that the wzx (O-antigen flippase) and wzy (O-antigen polymerase) genes were E. coli O121 specific, so regions in these two genes were chosen for development of PCR assays. The PCR assays using DNA from 99 E. coli O121 strains, strains representative of non-O121 E. coli serogroups, and strains of other bacterial genera and PCR assays using DNA from seven enrichments of swine fecal samples naturally contaminated with E. coli O121 showed specificity for E. coli O121. Thus, the PCR assay can be employed to reliably identify E. coli O121 and to potentially detect the organism in food, fecal, and environmental samples.