O-antigen biosynthesis gene clusters of Escherichia albertii: their diversity and similarity to Escherichia coli gene clusters and the development of an O-genotyping method.

Tadasuke Ooka,Yoshiki Etoh,Junichiro Nishi,Atsushi Iguchi,Takayuki Konno,Koichi Murakami,Naoko Imuta,Tetsuya Ikeda,Yasuhiro Gotoh,Yukiko Hara-Kudo,Kiyotaka Yoshiie,Kazuko Seto,Tetsuya Hayashi,Yoshitoshi Ogura,Mikiko Honda,Keiji Nakamura,Wakana Sugitani,Kimiko Kawano

doi:10.1099/mgen.0.000314

Abstract

Escherichia albertii is a recently recognized human enteropathogen that is closely related to Escherichia coli . In many Gram-negative bacteria, including E. coli , O-antigen variation has long been used for the serotyping of strains. In E. albertii , while eight O-serotypes unique to this species have been identified, some strains have been shown to exhibit genetic or serological similarity to known E. coli / Shigella O-serotypes. However, the diversity of O-serotypes and O-antigen biosynthesis gene clusters (O-AGCs) of E. albertii remains to be systematically investigated. Here, we analysed the O-AGCs of 65 E. albertii strains and identified 40 E. albertii O-genotypes (EAOgs) (named EAOg1–EAOg40). Analyses of the 40 EAOgs revealed that as many as 20 EAOgs exhibited significant genetic and serological similarity to the O-AGCs of known E. coli / Shigella O-serotypes, and provided evidence for the inter-species horizontal gene transfer of O-AGCs between E. albertii and E. coli . Based on the sequence variation in the wzx gene among the 40 EAOgs, we developed a multiplex PCR-based O-genotyping system for E. albertii (EAO-genotyping PCR) and verified its usefulness by genotyping 278 E. albertii strains from various sources. Although 225 (80.9 %) of the 278 strains could be genotyped, 51 were not assigned to any of the 40 EAOgs, indicating that further analyses are required to better understand the diversity of O-AGCs in E. albertii and improve the EAO-genotyping PCR method. A phylogenetic view of E. albertii strains sequenced so far is also presented with the distribution of the 40 EAOgs, which provided multiple examples for the intra-species horizontal transfer of O-AGCs in E. albertii .

Highlights

Escherichia albertii is a recently recognized human enteropathogen and an avian pathogen responsible for epidemic mortality [1,2,3]
This study identified 40 E. albertii O-g enotypes by analysing the O-antigen biosynthesis gene clusters (O-AGCs) of 65 E. albertii strains and provides what is believed to be the first insight into the diversity of E. albertii O-AGCs, as well as evidence for the horizontal transfer of O-AGCs within E. albertii, and between E. albertii and E. coli
To enrich the genome sequence and strain resources of E. albertii that can be used for the detailed analysis of O-A GCs and serotypes, we newly sequenced 11 E. albertii strains in this study

Summary

Introduction

Escherichia albertii is a recently recognized human enteropathogen and an avian pathogen responsible for epidemic mortality [1,2,3]. E. albertii strains carrying Shiga toxin (Stx) genes (stx2a or stx2f) have been identified [3, 7, 8], indicating that there is a significant risk of severe infections caused by this species. Another important aspect is that E. albertii infections have been underestimated because they have been frequently misidentified as enteropathogenic or enterohaemorrhagic Escherichia coli (EPEC or EHEC, respectively) due to their similarity in phenotypic and genetic features, such as biochemical properties and the possession of the locus of enterocyte effacement (LEE), encoding a type III secretion system (T3SS) [3]. Structural and serological changes in O-a ntigens can occur via point mutations in the genes in O-AGCs, such as glycosyltransferase genes, or by acquisition of O-antigen modification genes [19, 20]

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Conclusion