Genetic variation in the O-antigen gene cluster
Escherichia coli are classified by serotyping their polysaccharide (O) and flagellar (H) antigens. The gene cluster that encodes the O-antigen is conserved within O groups, which makes genes within the cluster attractive as targets for PCR assays and molecular serotyping. While the O-antigen molecular serotyping PCR assays are very sensitive and specific for the O-antigen type, they provide no additional genotype information about the strain. We sequenced either a part or the complete O-antigen gene cluster from Shiga toxin-containing E. coli (STEC) or non-STEC with different H serotypes from serogroups O26, O45, O103, O111, O121, O145, and O157 to identify potential polymorphism associated genotype information besides the O-antigen. At least one nucleotide polymorphism was identified from serogroups O45, O103, O111, O121, O145, and O157 that had a strong association with a strain being STEC or non-STEC while the serogroup O26 required two. For most of the serogroups, additional nucleotide polymorphisms in the gene cluster grouped non-STEC strains according to their H-antigen serotype. These serogroup specific nucleotide polymorphisms can be used to type serogroup O26, O45, O103, O111, O121, O145 and O157 strains and also predict whether they contain Shiga toxin-encoding genes.