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Infection and Immunity, November 2000, p. 6472-6477, Vol. 68, No. 11
Department of Microbiology and Immunology,
University of Melbourne, and Microbiological Research Unit, Murdoch
Children's Research Institute, Parkville, Victoria 3052, Australia
Received 27 March 2000/Returned for modification 15 June
2000/Accepted 7 August 2000
Attachment to the intestinal mucosa is an essential step in the
pathogenesis of diarrhea caused by enteropathogenic Escherichia coli (EPEC). Fimbriae and intimin, the outer membrane protein product of the chromosomal eae gene, contribute to this
process, but their relative roles and the nature of their interaction
are not known. The aim of this study was to determine the relative contribution of plasmid-encoded fimbriae, termed Ral, and intimin to
the capacity of rabbit-specific EPEC (REPEC) to attach to the intestinal mucosa of rabbits. To achieve this, we constructed a series
of mutants in REPEC strain 83/39 (O15:H
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Contribution of Plasmid-Encoded Fimbriae and Intimin to
Capacity of Rabbit-Specific Enteropathogenic Escherichia
coli To Attach to and Colonize Rabbit Intestine
), in which the ralE and eae genes were insertionally
inactivated. These strains were then inoculated into ligated loops of
rabbit ileum, which were resected 18 h later and examined by light
and electron microscopy. The results showed that intimin, but not Ral,
is essential for the elicitation of attaching-effacing lesions by
REPEC. Nevertheless, a
eae Ral-bearing mutant adhered to
the intestinal epithelium to the same extent as its
eae-positive parent and far more extensively than an
eae+
ral strain. To examine the contribution
of Ral and intimin to colonization of rabbit intestine, we fed these
strains to weanling rabbits, which were killed 4 days later, so that
the number of bacteria in various regions of the intestine could be
determined. The results indicated that strain 83/39 requires both Ral
and intimin to colonize the intestine successfully and that a
eae
ralE double mutant was incapable of colonizing
the intestine. Taken together, these findings indicate that Ral and
intimin act independently as adhesion factors of REPEC strain 83/39 and
that this strain carries no other significant colonization factor. When
both Ral and intimin are present, they appear to act cooperatively, with Ral-mediated adhesion preceding that mediated by intimin.
*
Corresponding author. Mailing address: Microbiological
Research Unit, Royal Children's Hospital, Parkville, Victoria 3052, Australia. Phone: (61-3) 9345-5741. Fax: (61-3) 9345-5764. E-mail: rbrowne{at}cryptic.rch.unimelb.edu.au.
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