Escherichia albertii Pathogenesis

Abstract

Escherichia albertii is an emerging enteropathogen of humans and many avian species. This bacterium is a close relative of Escherichia coli and has been frequently misidentified as enteropathogenic or enterohemorrhagic E. coli due to their similarity in phenotypic and genetic features, such as various biochemical properties and the possession of a type III secretion system encoded by the locus of enterocyte effacement. This pathogen causes outbreaks of gastroenteritis, and some strains produce Shiga toxin. Although many genetic and phenotypic studies have been published and the genome sequences of more than 200 E. albertii strains are now available, the clinical significance of this species is not yet fully understood. The apparent zoonotic nature of the disease requires a deeper understanding of the transmission routes and mechanisms of E. albertii to develop effective measures to control its transmission and infection. Here, we review the current knowledge of the phylogenic relationship of E. albertii with other Escherichia species and the biochemical and genetic properties of E. albertii, with particular emphasis on the repertoire of virulence factors and the mechanisms of pathogenicity, and we hope this provides a basis for future studies of this important emerging enteropathogen.

Figure 1

The phylogenetic position of E. albertii in the genus Escherichia. The neighbor-joining tree was constructed using the sequences of 111 single-copy genes that are fully conserved in the analyzed genomes of E. albertii (n = 34), E. coli (n = 44), E. fergusonii (n = 5), and other Escherichia species (n = 15). These genes show a low probability of recombination. The labels “A, B1, B2, D, and E” in E. coli indicate the major phylogroups of E. coli. These phylogroups include E. coli strains of various pathotypes. The figure was taken from our published article (14) with modifications.

Figure 2

The phylogenetic relationship of the 225 E. albertii strains genome-sequenced so far. The maximum-likelihood tree was reconstructed based on the core gene sequences (17). Strain names are indicated at each tip, and 14 completely sequenced strains are indicated. The information on the geographic distribution and isolation sources of the strains and the distribution of 40 EAOgs and virulence-related genes are also shown. The 7 EAOgs identified in both clades are indicated by triangles. The presence of LEE and ETT2 regions were determined by a tblastn search of the eae and eivG genes, respectively, as marker genes for each region.

Figure 3

Eight EAOgs highly homologous to the O-AGCs of known E. coli/Shigella O-serotypes. Shading and numbers between O-AGCs indicate the nucleotide sequence identities (%) of each gene. The figure was taken from our published article (17) with modifications.

Figure 4

Comparison of the gene organizations of the ETT2 region (A) and the genomic loci encoding flagellar biosynthesis- and chemotaxis-related genes (B and C, respectively) between E. albertii and E. coli. The amino acid sequence identities (A and C) and the nucleotide sequence identities (B) are presented. The dashed lines in (A) indicate the regions missing in each strain. The figure was taken from our published article (14) with modifications.

Figure 5

Transmission electron microscopy (TEM) image of rabbit ileal loop inoculated with the E. albertii 1551-2 strain. After 8 hours of inoculation, microvilli effacement and pedestal-like structures (asterisk) underneath adherent bacteria were demonstrated, thus confirming the ability of strain 1551-2 to induce AE lesion formation in vivo.