Three strains of enteropathogenic Escherichia coli (EPEC), originally isolated from humans and previously shown to cause diarrhea in human volunteers by unknown mechanisms, and one rabbit EPEC strain were shown to attach intimately to and efface microvilli and cytoplasm from intestinal epithelial cells in both the pig and rabbit intestine. The attaching and effacing activities of these EPEC were demonstrable by light microscopic examination of routine histological sections and by transmission electron microscopy. It was suggested that intact colostrum-deprived newborn pigs and ligated intestinal loops in pigs and rabbits may be useful systems to detect EPEC that have attaching and effacing activities and for studying the pathogenesis of such infections. The lesions (attachment and effacement) produced by EPEC in these systems were multifocal, with considerable animal-to-animal variation in response to the same strain of EPEC. The EPEC strains also varied in the frequency and extent of lesion production. For example, three human EPEC strains usually caused extensive lesions in rabbit intestinal loops, whereas two other human EPEC strains usually did not produce lesions in this system.

Cell-free culture filtrates of heat-labile enterotoxin-producing strains of Escherichia coli are capable of inducing morphological changes and steroidogenesis in monolayer cultures of adrenal cells. These tissue culture changes are simiar to those induced by cholera enterotoxin and cannot be effected by culture filtrates of other enterotoxigenic or enteropathogenic types of bacteria. The results of the tissue culture studies correlated well with those done in the standard intestinal-loop systems and suggest that this tissue culture system could be used to significantly aid epidemiological and molecular studies with heat-labile Escherichia coli enterotoxin.

We investigated the role of the rumen fermentation as a barrier to the foodborne pathogen, Escherichia coli O157:H7. Strains of E. coli, including several isolates of O157:H7, grew poorly in media which simulated the ruminal environment of a well-fed animal. Strains of E. coli O157:H7 did not display a superior tolerance to ruminal conditions which may facilitate their colonization of the bovine digestive tract. Unrestricted growth of E. coli was observed in rumen fluid collected from fasted cattle. Growth was inhibited by rumen fluid collected from well-fed animals. Well-fed animals appear less likely to become reservoirs for pathogenic E. coli. These results have implications for cattle slaughter practices and epidemiological studies of E. coli O157:H7.

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