Type 1 fimbriae and P pili (T1F (Type 1 fimbriae); Pap (P pili))

Type 1 fimbriae and P pili are prototypical chaperone-usher pathway (CUP) fimbrial structures on uropathogenic Escherichia coli (UPEC), enabling adhesion to host urinary tract tissues and promoting infection. Type 1 fimbriae (T1F), encoded by the fim operon (fimAICDFGH), form a 1-2 μm hair-like pilus with a helical rod of ~1000 FimA major subunits tipped by adaptor proteins (FimF, FimG) and the FimH adhesin, which binds mannosylated glycoproteins on bladder urothelium. P pili, encoded by the pap operon (papIBAHCDJKEFG), feature a similar structure with PapA rod subunits, PapH termination, and PapG adhesin targeting Gal(α1-4)Gal moieties in the kidney. Both undergo phase-variable expression regulated by invertible DNA switches (fimS for T1F), recombinases (FimB/E), and global factors like H-NS, Lrp, and PapB/PapI, responding to environmental cues. In disease, coordinated T1F (bladder) and P pilus (kidney) expression drives UPEC colonization, invasion, intracellular communities, and biofilms, evading clearance during urination via rod uncoiling as a molecular spring. No approved drugs directly target these structures, but their essential role in UTI pathogenesis positions them as validated antibacterial targets.

Other names

Type 1 fimbria (T1F, Fim)P fimbriae (P pilus, Pap pili)