Studies of escherichia coli in gnotobiotic pigs. IV. Comparison of enteropathogenic and nonenteropathogenic strains.

Four gnotobiotic pigs were infected with an enteropathogenic strain of Escherichia coli, and 4 were infected with a nonenteropathogenic strain of E. coli. Pigs killed in pairs at 6, 12, 24, and 48 hours PI. Four pigs were maintained as germfree controls. The discussions were based on the results of 1) clinical observations, 2) necropsy observations, 3) counts of viable E. coli in segments of the small intestine, 4) attempts to isolate E. coli from the heart, liver, and bile, 5) microscopic examination of fixed intestinal sections to determine the location of E. coli and morphologic evidence of the host response, and (6) determinations of the pH of the contents of the various portions of the gastrointestinal tract. No diarrhea, fluid accumulation, or impairment of the digestive capacity were noted in the pigs infected with the nonenteropathogenic strain of E. coli. The number of viable E. coli detected in the respective segments of the homogenized small intestine was similar in pigs infected with either strain. Diarrhea occurred continuously starting 18 hours PI in the pigs infected with the enteropathogenic strain and killed 24 or 48 hours PI. The pH of the contents of the cecum and colon became markedly more alkaline simultaneously with the increase in the heterogeneity and fluid content of the cecum and colon and thus appeared to correlate well with the onset of the clinical diarrhea. No enteritis was detected grossly or microscopically. The characteristics that determine the enteropathogenicity of a strain of E. coli could not be defined from the results, but it was noted that the host response appeared to be quite similar to that of infant rabbits experimentally infected with Vibrio cholera.