Abstract
Enterohemorrhagic Escherichia coli (EHEC) is a group of food-borne pathogens
that can cause diarrhea, colitis, and the hemolytic uremic syndrome
(HUS). The importance of several of the proposed EHEC virulence factors
lacks experimental verification in animal models. The limitations of
current animal models led us to reexamine the infant rabbit model for
the study of EHEC pathogenicity. Here, we report that intragastric
inoculation of a Shiga toxin 2 (Stx2)-producing E. coli
O157:H7 clinical isolate into infant rabbits led to severe diarrhea and
intestinal inflammation but no signs of HUS. We constructed a set of
isogenic derivatives of this isolate with deletions in several putative
virulence genes, including stx2, eae,
tir, and ehxA, to investigate the contribution of
individual virulence factors to EHEC pathogenicity.
stx2 increased the severity and duration of
EHEC-induced diarrhea. Furthermore, although stx2
had no role in EHEC intestinal colonization nor was it required for
EHEC-induced inflammation, stx2 altered how the
host responded to EHEC infection by promoting heterophilic infiltration
of the colonic epithelium and lamina propria. Intragastric inoculation
of purified Stx2 also induced inflammation and diarrhea in this model.
Diarrhea and intestinal inflammation were also dependent on EHEC
colonization, as EHEC derivatives with deletions in eae and
tir did not colonize, form attaching and effacing lesions, or
develop clinical signs of disease. Our studies indicate that infant
rabbits are a useful model for investigation of the intestinal stage of
EHEC pathogenesis and suggest that Shiga toxin may play a critical role
in causing diarrhea and inflammation in patients infected with
EHEC.