Iha: a novel Escherichia coli O157 : H7 adherence-conferring molecule encoded on a recently acquired chromosomal island of conserved structure

The mechanisms used by Shiga toxin (Stx)-producing Escherichia coli to adhe re to epithelial cells are incompletely understood. Two cosmids from an E. coli O157:H7 DNA library contain an adherence-conferring chromosomal gene e ncoding a protein similar to iron-regulated gene A (IrgA) of Vibrio cholera e (M. B. Goldberg, S. A. Boyko, J. R. Butterton, J. A. Stoebner, S, M. Payn e, and S, B, Calderwood, Mol. Microbiol. 6:2407-2418, 1992), We have termed the product of this gene the IrgA homologue adhesin (Iha), which is encode d by iha. Iha is 67 kDa in E. coli O157:H7 and 78 kDa in laboratory E. coli and is structurally unlike other known adhesins, DNA adjacent to iha conta ins tellurite resistance loci and is conserved in structure in distantly re lated pathogenic E. coli, but it is absent from nontoxigenic E. coli O55:H7 , sorbitol-fermenting Stx-producing E. coli O157:H-, and laboratory E. coli . We have termed this region the tellurite resistance- and adherence-confer ring island. me conclude that Iha is a novel bacterial adherence-conferring protein and is contained within an E. coli chromosomal island of conserved structure. Pathogenic E. coli O157:H7 has only recently acquired this isla nd.