Escherichia albertii sp. nov., a diarrhoeagenic species isolated from stool specimens of Bangladeshi children

Summary auto-generated

Researchers identified five diarrheal isolates from Bangladeshi children that were initially misclassified as Hafnia alvei but belong to the genus Escherichia. Using DNA-DNA hybridization, 16S rRNA sequencing, and phenotypic characterization, the isolates were found to constitute a homogeneous taxon with 82-100% internal DNA relatedness and 50.5-50.7 mol% G+C content. The strains showed 55-64% DNA relatedness to Escherichia coli and 54-60% to Shigella flexneri, but only 9-17% to H. alvei, definitively excluding the latter classification. All isolates possessed the eaeA gene typical of enteropathogenic E. coli and the species-specific phoE gene. They are phenotypically distinct from E. coli by lacking indole production and being unable to ferment lactose, D-sorbitol, or produce β-D-glucuronidase. The authors propose these strains represent a novel Escherichia species, named Escherichia albertii sp. nov., with type strain Albert 19982T. The organism is a diarrhoeagenic pathogen with potential significance for understanding enteric disease in developing countries.

Key findings

Five diarrheal isolates from Bangladesh represent a novel Escherichia species, Escherichia albertii sp. nov., with 82-100% internal DNA relatedness and 50.5-50.7 mol% G+C content
E. albertii shows 55-64% DNA relatedness to E. coli and 54-60% to Shigella flexneri but only 9-17% to Hafnia alvei, ruling out previous misclassification
The organism is phenotypically distinct from E. coli by negative indole and lactose/D-sorbitol fermentation and absence of β-D-glucuronidase production
E. albertii possesses the eaeA gene of enteropathogenic E. coli and the species-specific phoE gene, indicating pathogenic potential
All five isolates recovered from stool specimens of diarrheal children in Bangladesh between 1990-1991 represent a homogeneous diarrhoeagenic taxon

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Abstract

The taxonomic position of a group of five D-sorbitol- and lactose-negative enterobacterial isolates recovered from diarrhoeal stools of children at the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B), was investigated by DNADNA hybridization, phenotypic characterization and 16S rDNA sequencing. These strains were originally identified as Hafnia alvei-like with the API 20E system but, in fact, show more phenotypic and genotypic resemblance to members of the genus Escherichia. By 16S rDNA sequencing, one representative strain of the ICDDR,B group was shown to be closely affiliated to the genera Escherichia and Shigella. Using the fluorimetric microplate hybridization method, the diarrhoeagenic ICDDR,B isolates were found to constitute a homogeneous taxon (82 % internal DNA relatedness), with the closest affiliation to the type strains of Escherichia coli (5564 %) and Shigella flexneri (5460 %). The DNADNA hybridization levels were much lower with members of other described Escherichia species (1645 %) and with the type strain of H. alvei (917 %). The G+C content of the ICDDR,B strains ranged from 50·5 to 50·7 mol%. Together with the diagnostic characteristics reported previously, including the presence of the eaeA gene of enteropathogenic E. coli and of the E. coli and Shigella-specific phoE gene, it is concluded that the ICDDR,B strains represent a novel taxon in the genus Escherichia, for which the name Escherichia albertii sp. nov. is proposed. Its type strain is Albert 19982^T (=LMG 20976^T=CCUG 46494^T).