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.

Highlights

  • Over the last 30 years, enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 Sakai was the causing agent of hundreds of outbreaks of hemorrhagic colitis and hemolyticuremic syndrome (HUS)

  • This Tet-on approach enables the analysis of various fimbrial operons, Curli fimbriae and type 4 pili of E. coli O157:H7 Sakai in the nonpathogenic E. coli strain ORN172 (Woodall et al, 1993)

  • The highly variable and complex sets of fimbrial adhesins present in non-pathogenic and pathogenic E. coli strains are only poorly understood. For pathogenic strains, such as E. coli O157:H7 Sakai causing life-threatening infections, it is crucial to unravel the functions of all potential virulence factors to gain a better understanding of pathogenesis

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Summary

Introduction

Over the last 30 years, enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 Sakai was the causing agent of hundreds of outbreaks of hemorrhagic colitis and hemolyticuremic syndrome (HUS). The genetic locus of enterocyte effacement (LEE) harbors various virulence genes known to lead to attaching and effacing (A/E) lesions. These A/E lesions are caused by a type 3 secretion system (T3SS) which translocates the intimin receptor Tir, and effector proteins to host cells. E. coli O157:H7 Sakai possesses a complex set of adhesive structures including various fimbrial operons This set comprises 16 different fimbrial gene clusters: yeh-like, yad, sfm, ybg, ycb, type 3-like, Curli, F9, yeh, yfc, yra, lpf -like (lpf1), lpf (lpf2), fim, mat fimbriae and type 4 pili (Low et al, 2006). For most of these fimbrial adhesins, little is known about native expression conditions and knowledge of their role in virulence for EHEC Sakai is sparse

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