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

Abstract

<i>Escherichia albertii</i> is a recently recognized human enteropathogen that is closely related to <i>Escherichia coli</i>. In many Gram-negative bacteria, including <i>E. coli</i>, O-antigen variation has long been used for the serotyping of strains. In <i>E. albertii</i>, while eight O-serotypes unique to this species have been identified, some strains have been shown to exhibit genetic or serological similarity to known <i>E. coli</i>/<i>Shigella</i> O-serotypes. However, the diversity of O-serotypes and O-antigen biosynthesis gene clusters (O-AGCs) of <i>E. albertii</i> remains to be systematically investigated. Here, we analysed the O-AGCs of 65 <i>E. albertii</i> strains and identified 40 <i>E. albertii</i> 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 <i>E. coli</i>/<i>Shigella</i> O-serotypes, and provided evidence for the inter-species horizontal gene transfer of O-AGCs between <i>E. albertii</i> and <i>E. coli</i>. Based on the sequence variation in the <i>wzx</i> gene among the 40 EAOgs, we developed a multiplex PCR-based O-genotyping system for <i>E. albertii</i> (EAO-genotyping PCR) and verified its usefulness by genotyping 278 <i>E. albertii</i> 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 <i>E. albertii</i> and improve the EAO-genotyping PCR method. A phylogenetic view of <i>E. albertii</i> 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 <i>E. albertii</i>.