DNA Sequence and Analysis of the O-antigen Gene Clusters of Escherichia coli Serogroups O62 O68 O131 O140 O142 and O163 and Serogroup-Specific PCR Assays

摘要

The DNA sequence of the O-antigen gene clusters of Escherichia coli serogroups O62, O68, O131, O140, O142, and O163 was determined. There were 9 to 12 open reading frames (ORFs) identified, encoding genes required for O-antigen sugar biosynthesis, transfer, and processing. Primers based on the wzx (O-antigen flippase) and wzy (O-antigen polymerase) genes within the O-antigen gene clusters were designed and used in PCR assays to identify each serogroup. Of interest, an NCBI BLAST alignment showed that the O-antigen gene cluster of O62 shares a 99% sequence identity with O68, with the exception of an insertion sequence (IS) element between the rmlA and rmlC genes of O62. The IS insertion in O62 infers that O68 may be the ancestor of O62. Specificity testing using strains belonging to each of the serogroups isolated from various sources, representative standard strains of 174 E. coli O serogroups, and 16 non-E. coli bacteria revealed that the PCR assays were specific for each serogroup. The PCR assay targeting O62 also gave positive results with strains serotyped as E. coli O68, which confirms that the O-antigen gene cluster sequences for these two serogroups are very similar. The PCR assays developed in this study can be used for the detection and identification of E. coli O62, O68, O131, O140, O142, and O163 strains isolated from different sources.