Adhesive threads of extraintestinal pathogenic Escherichia coli Original paper

What was reviewed?

This review describes adhesive threads of extraintestinal pathogenic Escherichia coli and explains how a wide range of fimbrial and afimbrial adhesins support colonization and disease at sites outside the gut. The authors focus on ExPEC pathotypes such as uropathogenic, newborn meningitic, septicaemia associated and avian pathogenic strains and show that these lineages arise mainly from phylogenetic group B2 and to a lesser extent from group D. They summarize in detail the structure, genetics and receptor specificity of major adhesins, including type 1 fimbriae, P fimbriae, curli fibres, S fimbriae, F1C fimbriae, Dr fimbriae, afimbrial adhesins, temperature sensitive haemagglutinin and newer trimeric autotransporter and yqi encoded systems. The review then links these adhesive systems to specific host receptors, such as mannose-containing glycoconjugates, P blood group antigens, sialylated glycoconjugates, and glycosphingolipids.

Who was reviewed?

The review draws on molecular, epidemiological, and experimental data from human and animal extraintestinal pathogenic Escherichia coli isolates and compares them with commensal and intestinal pathogenic strains. It includes work on uropathogenic strains from women and children with cystitis and pyelonephritis, newborn meningitis isolates from infants with sepsis and meningitis, and avian pathogenic strains from poultry with colisepticaemia, as well as septicaemia-associated strains from diverse hosts. The authors discuss phylogenetic analyses that show enrichment of these adhesins in B2 and D lineages and highlight the frequent co-occurrence of multiple adhesin systems within single ExPEC genomes. They also describe in vitro and in vivo infection models that use human bladder and kidney epithelium, brain endothelial cells, chicken tracheal and gut explants, and animal infection models in chicks, mice, and other species to define how each adhesin contributes to colonization, tissue tropism, and virulence.

Most important findings

The review shows that ExPEC strains carry a rich and diverse adhesin repertoire and that adhesive threads of extraintestinal pathogenic Escherichia coli form a key virulence platform that supports both gut colonization and spread to extraintestinal sites. Type 1 fimbriae, present in most ExPEC, mediate mannose-sensitive binding to urinary and intestinal epithelia and show phase variable expression and strong selection on the FimH adhesin, which improves binding to monomannose receptors and enhances urinary tract colonization. P fimbriae bind Galα(1–4)Gal containing P blood group antigens.

Curli fibres bind extracellular matrix proteins, promote biofilm formation and internalisation into eukaryotic cells, and occur in almost all avian ExPEC strains, suggesting an essential role in persistent carriage and tissue invasion. Dr fimbriae and related afimbrial adhesins bind decay accelerating factor and Dr blood group antigens and associate with chronic urinary tract infection, pregnancy-related complications, and tubulointerstitial nephritis. The review introduces ExPEC Adhesin I, encoded by yqi, as a novel fimbrial system prevalent in more than half of ExPEC isolates, concentrated in B2 and ST95 lineages, and essential for colonization in avian models, which makes it a promising marker and target. Notably, the authors highlight evidence that some of these adhesins also mediate binding to colonic and ileal enterocytes and support intestinal colonization in chickens and piglets, suggesting that adhesive profiles form part of a microbiome signature that links gut reservoirs to subsequent urinary, respiratory or systemic disease.

Key implications

For clinicians, this review indicates that adhesive threads of extraintestinal pathogenic Escherichia coli are central determinants of host colonization, tissue tropism, and the transition from asymptomatic gut carriage to invasive disease, which means that adhesin repertoires are relevant both for pathogenesis and for microbiome-based risk assessment. The strong association of particular adhesins and phylogenetic backgrounds with urinary tract infection, neonatal meningitis, and avian septicaemia suggests that detection of adhesin gene combinations such as fimH, pap, sfa, foc, dra, tsh, and yqi, together with B2 or D assignment, could help to define high-risk ExPEC clones in intestinal or environmental samples. From a therapeutic perspective, the review supports adhesins as vaccine and antibody targets, since blocking receptor binding at mucosal surfaces can prevent initial colonization and reduce bacterial spread, as already shown for FimH and P fimbriae in animal models.