Association of cytolethal distending toxin-II gene-positive Escherichia coli with Escherichia albertii, an emerging enteropathogen

Abstract Cytolethal distending toxin (CDT)-producing Escherichia coli have been isolated from patients with diarrhea, sepsis and urinary tract infection. CDT of E. coli is divided into five types (CDT-I through CDT-V) based on differences in amino acid sequences and its genomic location. However, in our recent studies, a few strains of cdt-II gene-positive bacteria, initially identified as atypical E. coli, were re-identified as Escherichia albertii , an emerging enteropathogen, by extensive characterization including multilocus sequence (MLS) analysis and sugar utilization tests. This finding prompted us to investigate if bacteria previously identified as cdt-II gene-positive E. coli might be E. albertii . In the present study, we therefore re-examined the identity of 20 cdt-II gene-positive bacteria isolated from children with diarrhea, which were initially identified as atypical E. coli . By extensive sugar utilization tests, these bacteria showed a closer relatedness to E. albertii than E. coli , because they did not ferment any of the tested sugars including dulcitol, lactose, d -melibiose, l -rhamnose and d -xylose. Further, both phylogenetic analyses based on nucleotide sequences of 7 housekeeping genes (MLS analysis) and rpoB gene showed that all the cdt-II gene-positive bacteria belonged to a distinct lineage of E. albertii from those of E. coli and Shigella boydii . They were also positive by an E. albertii -specific PCR. Taken together, these data suggest that cdt-II gene-positive bacteria previously identified as E. coli are actually E. albertii . Therefore, we suggest a new definition for cdt-II gene-positive E. coli as E . albertii with the inclusion of CDT-II in E . albertii CDT.