Expression and Functional Characterization of Various Chaperon-Usher Fimbriae, Curli Fimbriae, and Type 4 Pili of Enterohemorrhagic Escherichia coli O157:H7 Sakai

Abstract

Enterohemorrhagic Escherichia coli (EHEC) is a highly pathogenic strain leading to hemorrhagic colitis and to the hemolytic-uremic syndrome (HUS) in humans. The mechanisms by which pathogenic E. coli infect and colonize humans leading to the typical disease pattern are in focus of many investigations. The adhesion of EHEC to epithelial cells by the coordinated translocation of receptor Tir and surface expression of corresponding adhesin intimin is a key event in host-pathogen-interaction. However, less is known about other adhesins encoded by EHEC, especially about the complex set of fimbrial adhesins varying among various serotypes. Here, we investigate EHEC serotype O157:H7 strain Sakai possessing at least 16 putative fimbrial gene clusters. Using a synthetic heterologous expression system in a non-pathogenic E. coli strain, a subset of 6 gene clusters for fimbrial adhesins was analyzed. We were able to visualize surface expression of two γ1 class fimbriae (Fim and Ycb), two γ4 class fimbriae (Yad and Yeh), and two fimbrial adhesins which are assembled by the nucleation/precipitation pathway (Curli fimbriae), and by a type 2 secretion system (type 4 pili). Further, we elucidated the impact of these fimbrial adhesins in adhesion to various epithelial cells lines (HeLa, MDCK, and CaCo2), and the contribution on biofilm formation. We demonstrate the ultrastructure of Fim fimbriae and Yad fimbriae of EHEC Sakai, and Yeh fimbriae of E. coli in general. The involvement of Fim fimbriae of EHEC Sakai to adhesion to various epithelial cell lines, and contribution to biofilm formation is reported here. Our approach provides first ultrastructural and functional data for novel EHEC adhesins, and enables further understanding of the involvement of fimbrial adhesins in pathogenesis of EHEC Sakai.

Escherichia coli 0157:H7 virulence factors and the ruminant reservoir

“…The initial contact of E. coli O157:H7 with enterocytes involves nonintimin adhesion factors acting in accordance with temporal suppression of flagella expression. Curli fimbriae-associated amyloid fibers, assembled on the bacterial surface, congribute to E. coli O157:H7 biofilm formation and attachment to both human and bovine cells [48][49][50][51]. Curli expression and motility are conversely regulated by the PchE transcriptional factor.…”

Electron cryo-microscopy reveals the structure of the archaeal thread filament

“…In bacteria, a large variety of adhesive filaments have been well studied. These include chaperone-usher (CU), curli, type-IV (T4P) and type-V pili (T5P) in Gram-negative bacteria, and sortase-dependent pili in Gram-positive bacteria [5][6][7][8][9][10][11] .In archaea, cell adhesion and biofilm formation are far less understood. So far, the best studied archaeal adhesive filaments are of the type-IV pilus superfamily (T4FF) [12][13][14][15] .…”

“…In bacteria, a large variety of adhesive filaments have been well studied. These include chaperone-usher (CU), curli, type-IV (T4P) and type-V pili (T5P) in Gram-negative bacteria, and sortase-dependent pili in Gram-positive bacteria [5][6][7][8][9][10][11] .…”

Fim3-dependent autoagglutination of Bordetella pertussis

“…Several prior experiments demonstrated that type 1 fimbriae were implicated in autoagglutination and binding. For instance, expressions of the type 1 fimbriae, Curli and FimH, lead to autoagglutination in Escherichia coli 13 – 15 . Farfan et al (2011) found that Lpf fimbriae binds the extracellular matrix (ECM) proteins of the host cell.…”