Adherent-invasive Escherichia coli are a leading candidate bacterial trigger for Crohn's disease (CD).
The Adherent-invasive Escherichia coli pathovar is defined by in vitro cell-line assays examining specific bacteria/cell interactions.
No molecular marker exists for their identification.
Dr Claire O'Brien and colleagues identified a molecular property common to the Adherent-invasive Escherichia coli phenotype.
The team isolated 41 B2 phylogroup Escherichia coli strains from 36 Australian subjects, including 19 patients with IBD and 17 without.
Adherence/invasion assays were conducted using the I-407 epithelial cell line and survival/replication assays using the THP-1 macrophage cell line.
Cytokine secretion tumor necrosis factor was measured using ELISA.
The research team noted that genomes were assembled and annotated, and cluster analysis performed using CD-HIT.
The resulting matrices were analyzed to identify genes unique/more frequent in adherent-invasive Escherichia coli strains compared with non-adherent-invasive Escherichia coli strains.
Of all B2 phylogroup strains assessed, the team observed that 79% could survive and replicate in macrophages.
Among them, 11/41 strains also adhere to and invade epithelial cells, a phenotype assigning them to the adherent-invasive Escherichia coli pathovar.
The adherent-invasive Escherichia coli strains were phylogenetically heterogeneous.
The researchers did not identify a gene common to all, or the majority of, adherent-invasive Escherichia coli.
Cytokine secretion and CRISPRs were not associated with the adherent-invasive Escherichia coli phenotype.
Dr O'Brien's team concludes, "Comparative genomic analysis of adherent-invasive Escherichia coli and non-adherent-invasive Escherichia coli strains did not identify a molecular property exclusive to the adherent-invasive Escherichia coli phenotype."
"We recommend a broader approach to the identification of the bacteria-host interactions that are important in the pathogenesis of Crohn's disease."