Studies of escherichia coli in gnotobiotic pigs. V. Evaluation of the effects of oral and parenteral administration of immune serum.

The effects of orally and/or parenterally administered immune serums were evaluated in 36 gnotobiotic pigs infected with an enteropathogenic strain of Escherichia coli. Pigs were euthanatized at predetermined time intervals between 6 and 48 hours prostinfection. The results were evaluated on the basis 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) determination of the pH of the various portions portions of the gastrointestinal tract. Orally administered immune serum completely protected the pigs from fluid loss and diarrhea. Parenterally administered serum did not protect against fluid loss into the intestinal lumen but diarrhea was not observed. The pH of the contents of the lumen of the cecum and colon was markedly elevated simultaneously with the accumulation of fluids and incompletely digested milk. The results of microscopic examination of tissues as well as other determinations did not reveal the mechanism of fluid loss nor the mechanism of protection afforded by orally administered immune serum. The results support the contention that continuous adequate levels of appropriate antibodies in the lumen of the intestinal tract aŕe a significant deterrant to the establishment of colibacillosis in baby pigs.