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Genomic comparison of the O-antigen biosynthesis gene clusters of Escherichia coli O55 strains belonging to three distinct lineages

¹ Division of Bioenvironmental Science, Frontier Science Research Center, University of Miyazaki, 5200 Kiyotake, Miyazaki 889-1692, Japan
² Division of Microbiology, Department of Infectious Disease, Faculty of Medicine, University of Miyazaki, 5200 Kiyotake, Miyazaki 889-1692, Japan
³ Division of Cell and Molecular Biology, Imperial College London, London SW7 2AZ, UK

Correspondence
Tetsuya Hayashi
thayash{at}med.miyazaki-u.ac.jp

Typical enteropathogenic Escherichia coli (EPEC) O55 : H7 is regarded as the closest relative of enterohaemorrhagic E. coli (EHEC) O157 : H7. Both serotypes usually express the 1 intimin subclass and trigger actin polymerization by the Tir-TccP pathway. However, atypical O55 : H7 strains capable of triggering actin polymerization via the Tir-Nck pathway have recently been identified. In this study, we investigated the genotypic differences and phylogenetic relationships between typical and atypical O55 : H7 strains. We show that the atypical O55 : H7 strains, which express the intimin subclass and lack both tccP and tccP2, belong to an E. coli lineage distinct from the typical O55 : H7 and from the EPEC O55 : H6, which also uses the Tir-Nck actin polymerization pathway. We conducted genomic comparisons of the chromosomal regions covering the O-antigen gene cluster and its flanking regions between the three O55 lineages by RFLP analysis of PCR products and DNA sequencing analysis of about 65 kb chromosomal regions. This unexpectedly revealed that horizontal transfer of large fragments (40 kb) encoding the O55-antigen gene cluster and part of the neighbouring colanic acid gene cluster was involved in the emergence of the three O55 E. coli lineages. The data provide new insights into the mechanisms involved in the generation of a wide variety of O-serotypes in Gram-negative bacteria.

The GenBank/EMBL/DDBJ accession numbers for the sequences reported in this paper are AB334576–AB334719 (housekeeping genes), AB334558–AB334567 (eae), AB355995–AB356000 (tccP), AB356001 (tccP2), AB334568–AB334575 (fliC) and AB353131–AB353133 (O55-antigen gene clusters and their flanking regions). The GEO accession number for the microarray data reported in this paper is GSE8889.

A supplementary figure and table are available with the online version of this paper.

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