Cloning, expression, and characterization of fimbrial operon F9 from enterohemorrhagic Escherichia coli O157:H7

Alison S. Low, Francis Dziva, Alfredo G. Torres, Jessenya L. Martinez, Tracy Rosser, Stuart W. Naylor, Kevin Spears, Nicola Holden, Arvind Mahajan, John Findlay, Jill Sales, David George Emslie Smith, J. Christopher Low, Mark P. Stevens, David L. Gally

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Recent transposon mutagenesis studies with two enterohemorrhagic Escherichia coli (EHEC) strains, a sero- type O26:H- strain and a serotype O157:H7 strain, led to identification of a putative fimbrial operon that promotes colonization of young calves (1 to 2 weeks old). The distribution of the gene encoding the major fimbrial subunit present in O-island 61 of EHEC O157:H7 in a characterized set of 78 diarrheagenic E. coli strains was determined, and this gene was found in 87.2% of the strains and is therefore not an EHEC-specific region. The cluster was amplified by long-range PCR and cloned into the inducible expression vector pBAD18. Induced expression in E. coli K-12 led to production of fimbriae, as demonstrated by transmission electron microscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The fimbriae were purified, and sera to the purified major subunit were raised and used to demonstrate expression from wild-type E. coli O157:H7 strains. Induced expression of the fimbriae, designated F9 fimbriae, was used to characterize binding to bovine epithelial cells, bovine gastrointestinal tissue explants, and extracellular matrix components. The fimbriae promoted increases in the levels of E. coli K-12 binding only to bovine epithelial cells. In contrast, induced expression of F9 fimbriae in E. coli O157:H7 significantly reduced adherence of the bacteria to bovine gastrointestinal explant tissue. This may have been due to physical hindrance of type III secretion-dependent attachment. The main F9 subunit gene was deleted in E. coli O157:H7, and the resulting mutant was compared with the wild-type strain for colonization in weaned cattle. While the shedding levels of the mutant were reduced, the animals were still colonized at the terminal rectum, indicating that the adhesin is not responsible for the rectal tropism observed but may contribute to colonization at other sites, as demonstrated previously with very young animals.

Original languageEnglish
Pages (from-to)2233-2244
Number of pages12
JournalInfection and Immunity
Issue number4
Publication statusPublished - Apr 2006


  • Animals
  • Bacterial Adhesion
  • Cattle
  • Cells, Cultured
  • Cloning, Molecular
  • Escherichia coli K12
  • Escherichia coli O157
  • Escherichia coli Proteins
  • Extracellular Matrix
  • Fimbriae, Bacterial
  • Gene Deletion
  • Genes, Bacterial
  • Operon
  • Rectum


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