Higher frequency of adherent-invasive Escherichia coli within a sub- group of B2 phylogroup strains

Abstract

Background Adherent-invasive E. coli (AIEC) are associated with Crohn’s disease. There is no defining molecular characteristic of these strains, and identification relies on laborious phenotypic testing. A recent AIEC genome comparison study of ours showed that AIEC strains belonging to sequence type 95 (ST95) of the B2 phylogroup, with an O18:H7 serotype, are more likely to be AIEC. The aim of this study was to compare a larger set of ST95 strains, to determine whether or not AIEC strains are non-randomly distributed within ST95.

Methods We conducted a genome comparison of 217 ST95 E. coli strains: 7 AIEC; 11 non-AIEC; and 199 strains that have not been phenotyped. Of the 217 genomes, 140 were publicly available, 77 were our own and were sequenced using various sequencing platforms and had at least 50 X coverage. All genomes were aligned and phylogenetically compared using the Harvest software suite (v. 1.2). The frequency of AIEC strains within the various ST95 subgroups was compared.

Results AIEC strains were non-randomly distributed within ST95, with the majority (71%) of AIEC strains belonging to the same ST95 sub-group, and having the O18:H7 serotype.

Conclusion Although a molecular marker does not exist for identifying all AIEC, further AIEC phenotyping and genome comparisons of ST95 O18:H7 strains may reveal a molecular marker for this sub-group, which are significantly more likely to be AIEC.