Functional studies of intimin in vivo and ex vivo: implications for host specificity and tissue tropism

Abstract

Intimin is an outer-membrane adhesin that is essential for colonization of the host gastrointestinal tract by attaching and effacing pathogens including enteropathogenic Escherichia coli (EPEC), enterohaemorrhagic E. coli (EHEC) and Citrobacter rodentium (CR). The N-terminus of intimin from the different strains is highly conserved while the C-terminus, which harnesses the active receptor-binding site, shows sequence and antigenic polymorphism. This diversity was used to define a number of distinct intimin types, the most common of which are α, β and γ. Intimin binds the type III secretion system effector protein Tir. However, a large body of evidence suggests that intimin also binds a host-cell-encoded receptor(s) (Hir), and interaction of different intimin types with Hir contributes to tissue and host specificity. The aims of this study were to compare the activity of the major intimin types (α, β and γ) in vivo and ex vivo, using the CR mouse model and in vitro organ culture (IVOC), and to determine their exchangeability. The results confirm that intimin γ is not functional in the CR mouse model. In the pig, intimin β can substitute for EPEC intimin α but when placed in an EHEC O157 : H7 background it does not produce an intimin α-like tropism, although some adhesion to the small and large intestine was observed. In contrast, in human IVOC, intimin β in an EHEC background produces small intestinal colonization in a similar manner to intimin α.

Pathogenesis of Human Enterovirulent Bacteria: Lessons from Cultured, Fully Differentiated Human Colon Cancer Cell Lines

“…Phillips and coworkers have established an IVOC from pediatric biopsy specimens of duodenum mounted in a modified MicroSnapwell system specifically adapted for use with 2-to 3-mmdiameter biopsy samples. This IVOC system has been used mainly to study the mechanisms of virulence of ETEC (839), EPEC (840)(841)(842)(843)(844)(845)(846)(847)(848)(849)(850)(851), EHEC (852)(853)(854)(855)(856)(857), EAEC (507,858), and Salmonella (392) and the action of Stx toxins (641). Other IVOCs have been used for studies on C. jejuni (859), EPEC (692,860,861), EAEC (645,(862)(863)(864), and Shigella (865) pathogenesis.…”

Type 2 Secretion Promotes Enterohemorrhagic Escherichia coli Adherence and Intestinal Colonization

“…Numerous EHEC genes have been shown to be important for adherence of this pathogen to tissue culture monolayers (60) and animal intestinal explants (34,48) and to promote persistence in ruminant reservoir hosts (10,11); however, with the exception of proteins encoded in the LEE pathogenicity island (9,43,44), the roles of candidate adhesion factors in animal models of disease are not known. Here, we identified three EHEC genes (adfO [Z2053], located on prophage CP-933O; yodA, a gene also found in E. coli K-12; and etpC, a gene located on pO157) that contribute to adherence of EHEC to HeLa cell monolayers.…”

In Vitro and In Vivo Model Systems for Studying Enteropathogenic Escherichia coli Infections

“…In addition, the variability in sample properties between donors and results is far greater than in cell line models. The IVOC system has been used to study EPEC-host specificity and tissue tropism (Girard et al 2005;Mundy et al 2007), Tir-intimin-dependent colonization and A/E lesion formation (Frankel et al 1998a;Schüller et al 2007;Frankel and Phillips 2008). The polarized IVOC method has shown that apical EPEC infection of duodenal mucosa results in a flagellin-dependent increase in IL-8 levels (Schüller et al 2009).…”