Ucl fimbriae regulation and glycan receptor specificity contribute to gut colonisation by extra-intestinal pathogenic Escherichia coli

Abstract

Extra-intestinal pathogenic Escherichia coli (ExPEC) belong to a critical priority group of antibiotic resistant pathogens. ExPEC establish gut reservoirs that seed infection of the urinary tract and bloodstream, but the mechanisms of gut colonisation remain to be properly understood. Ucl fimbriae are attachment organelles that facilitate ExPEC adherence. Here, we investigated cellular receptors for Ucl fimbriae and Ucl expression to define molecular mechanisms of Ucl-mediated ExPEC colonisation of the gut. We demonstrate differential expression of Ucl fimbriae in ExPEC sequence types associated with disseminated infection. Genome editing of strains from two common sequence types, F11 (ST127) and UTI89 (ST95), identified a single nucleotide polymorphism in the ucl promoter that changes fimbriae expression via activation by the global stress-response regulator OxyR, leading to altered gut colonisation. Structure-function analysis of the Ucl fimbriae tip-adhesin (UclD) identified high-affinity glycan receptor targets, with highest affinity for sialyllacto-N-fucopentose VI, a structure likely to be expressed on the gut epithelium. Comparison of the UclD adhesin to the homologous UcaD tip-adhesin from Proteus mirabilis revealed that although they possess a similar tertiary structure, apart from lacto-N-fucopentose VI that bound to both adhesins at low-micromolar affinity, they recognize different fucose- and glucose-containing oligosaccharides. Competitive surface plasmon resonance analysis together with co-structural investigation of UcaD in complex with monosaccharides revealed a broad-specificity glycan binding pocket shared between UcaD and UclD that could accommodate these interactions. Overall, our study describes a mechanism of adaptation that augments establishment of an ExPEC gut reservoir to seed disseminated infections, providing a pathway for the development of targeted anti-adhesion therapeutics.

Distinct ecological fitness factors coordinated by a conserved Escherichia coli regulator during systemic bloodstream infection

“…This creates multiple scenarios in which UPEC could potentially benefit from positively regulating fimbrial adhesion during BSI. Furthermore, our work raises the possibility that other fimbriae types associated with UPEC disease, such as P fimbriae and Ucl fimbriae, which are located on pathogenicity-associated genomic islands, may also be subjected to complex regulatory control by conserved TFs located on the core chromosome ( 54 – 56 ).…”

The bacterial genetic determinants of Escherichia coli capacity to cause bloodstream infections in humans

“…Also, differences between E . coli lineages have been described [ 40 , 79 , 80 ]. In the latter cases concerning differential expression of fimbriae (ECP, Ucl and P fimbriae, respectively), causal SNPs in the gene promoter region were identified.…”

Combined functional genomic and metabolomic approaches identify new genes required for growth in human urine by multidrug-resistant Escherichia coli ST131

“…Chromosomal DNA purification, PCR, and DNA sequencing of PCR products were performed as previously described ( 65 ). Defined mutations were made using the λ-Red recombinase method with some modifications as previously described ( 22 , 66 , 67 ). Complementation was performed by cloning the gene of interest into a gentamicin-resistant derivative of pSU2718 ( 68 ) at appropriate cut sites.…”