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Intimin type influences the site of human intestinal mucosal colonisation by enterohaemorrhagic Escherichia coli O157:H7.

ABSTRACT: BACKGROUND:Enterohaemorrhagic (EHEC) and enteropathogenic (EPEC) Escherichia coli epithelial cell adhesion is characterised by intimate attachment, and attaching and effacing (A/E) lesion formation. This event is mediated in part by intimin binding to another bacterial protein, Tir (translocated intimin receptor), which is exported by the bacteria and integrated into the host cell plasma membrane. Importantly, EPEC (O127:H6) and EHEC (O157:H7) express antigenically distinct intimin types known as intimin alpha and gamma, respectively. EHEC (O157:H7) colonises human intestinal explants although adhesion is restricted to the follicle associated epithelium of Peyer's patches. This phenotype is also observed with EPEC O127:H6 engineered to express EHEC intimin gamma. AIMS:To investigate the influence of intimin on colonisation of human intestine by E coli O157:H7, and intimin types on tissue tropism in humans. METHODS:Human intestinal in vitro organ culture with wild type and mutant strains of O157:H7 were employed. RESULTS:Introducing a deletion mutation in the eae gene encoding intimin gamma in EHEC (O157:H7) caused the strain (ICC170) to fail to colonise human intestinal explants. However, colonisation of Peyer's patches and A/E lesion formation were restored with intimin gamma expression from a plasmid (ICC170 (pICC55)). In contrast, complementing the mutation with intimin alpha resulted in a strain (ICC170 (pCVD438)) capable of colonising and producing A/E lesions on both Peyer's patch and other small intestinal explants. CONCLUSION:Intimin is necessary for human intestinal mucosal colonisation by E coli O157:H7. Intimin type influences the site of colonisation in a Tir type independent mechanism; intimin gamma appears to restrict colonisation to human follicle associated epithelium.

SUBMITTER: Fitzhenry RJ

PROVIDER: S-EPMC1773112 | biostudies-literature | 2002 Feb

REPOSITORIES: biostudies-literature

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Intimin type influences the site of human intestinal mucosal colonisation by enterohaemorrhagic Escherichia coli O157:H7.

Fitzhenry R J RJ Pickard D J DJ Hartland E L EL Reece S S Dougan G G Phillips A D AD Frankel G G

Gut 20020201 2

<h4>Background</h4>Enterohaemorrhagic (EHEC) and enteropathogenic (EPEC) Escherichia coli epithelial cell adhesion is characterised by intimate attachment, and attaching and effacing (A/E) lesion formation. This event is mediated in part by intimin binding to another bacterial protein, Tir (translocated intimin receptor), which is exported by the bacteria and integrated into the host cell plasma membrane. Importantly, EPEC (O127:H6) and EHEC (O157:H7) express antigenically distinct intimin types ...[more]

PMID: 11788556

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Project description:The bovine gastrointestinal (GI) tract is the main reservoir for enterohaemorrhagic Escherichia coli (EHEC) responsible for food-borne infections. Characterization of nutrients preferentially used by EHEC in the bovine intestine would help to develop ecological strategies to reduce EHEC carriage. However, the carbon sources that support the growth of EHEC in the bovine intestine are poorly documented. In this study, a very low concentration of glucose, the most abundant monomer included in the cattle dietary polysaccharides, was detected in bovine small intestine contents (BSIC) collected from healthy cows at the slaughterhouse. Six carbohydrates reported to be included in the mucus layer covering the enterocytes [galactose, N-acetyl-glucosamine (GlcNAc), N-acetyl- galactosamine (GalNAc), fucose, mannose and N-acetyl neuraminic acid (Neu5Ac)] have been quantified for the first time in BSIC and accounted for a total concentration of 4.2?mM carbohydrates. The genes required for enzymatic degradation of the six mucus-derived carbohydrates are highly expressed during the exponential growth of the EHEC strain O157:H7 EDL933 in BSIC and are more strongly induced in EHEC than in bovine commensal E.?coli. In addition, EDL933 consumed the free monosaccharides present in the BSIC more rapidly than the resident microbiota and commensal E.?coli, indicating a competitive ability of EHEC to catabolize mucus-derived carbohydrates in the bovine gut. Mutations of EDL933 genes required for the catabolism of each of these sugars have been constructed, and growth competitions of the mutants with the wild-type strain clearly demonstrated that mannose, GlcNAc, Neu5Ac and galactose catabolism confers a high competitive growth advantage to EHEC in BSIC and probably represents an ecological niche for EHEC strains in the bovine small intestine. The utilization of these mucus-derived monosaccharides by EDL933 is apparently required for rapid growth of EHEC in BSIC, and for maintaining a competitive growth rate as compared with that of commensal E.?coli. The results suggest a strategy for O157:H7 E.?coli survival in the bovine intestine, whereby EHEC rapidly consumes mucus-derived carbohydrates that are poorly consumed by bacteria belonging to the resident intestinal microbiota, including commensal E.?coli.

Project description:Enterohaemorrhagic Escherichia coli (EHEC) are responsible for outbreaks of food- and water-borne illness. The bovine gastrointestinal tract (GIT) is thought to be the principle reservoir of EHEC. Knowledge of the nutrients essential for EHEC growth and survival in the bovine intestine may help in developing strategies to limit their shedding in bovine faeces thus reducing the risk of human illnesses. To identify specific metabolic pathways induced in the animal GIT, the transcriptome profiles of EHEC O157:H7 EDL933 during incubation in bovine small intestine contents (BSIC) and minimal medium supplemented with glucose were compared. The transcriptome analysis revealed that genes responsible for the assimilation of ethanolamine, urea, agmatine and amino acids (Asp, Thr, Gly, Ser and Trp) were strongly up-regulated suggesting that these compounds are the main nitrogen sources for EHEC in BSIC. A central role for the gluconeogenesis pathway and assimilation of gluconeogenic substrates was also pinpointed in EHEC incubated in BSIC. Our results suggested that three amino acids (Asp, Ser and Trp), glycerol, glycerol 3-phosphate, L-lactate and C4-dicarboxylates are important carbon sources for EHEC in BSIC. The ability to use gluconeogenic substrates as nitrogen sources (amino acids) and/or carbon sources (amino acids, glycerol and lactate) may provide a growth advantage to the bacteria in intestinal fluids. Accordingly, aspartate (2.4 mM), serine (1.9 mM), glycerol (5.8 mM) and lactate (3.6 mM) were present in BSIC and may represent the main gluconeogenic substrates potentially used by EHEC. A double mutant of E. coli EDL933 defective for phosphoenolpyruvate synthase (PpsA) and phosphoenolpyruvate carboxykinase (PckA), unable to utilize tricarboxylic acid (TCA) intermediates was constructed. Growth competition experiments between EHEC EDL933 and the isogenic mutant strain in BSIC clearly showed a significant competitive growth advantage of the wild-type strain further illustrating the importance of the gluconeogenesis pathway in maintaining EHEC in the bovine GIT.

Dataset Information

Intimin type influences the site of human intestinal mucosal colonisation by enterohaemorrhagic Escherichia coli O157:H7.

Publications

Intimin type influences the site of human intestinal mucosal colonisation by enterohaemorrhagic Escherichia coli O157:H7.

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