Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Veterinary Pathology


When isolated small intestinal epithelial cells of neonatal and older pigs, calves, and mice were mixed with enterotoxigenic Escherichia coli (ETEC), strain 263 (08:K87,88ab:H19) adhered well to epithelial cells from animals in each age group while strains 431 (0101:K30,99:NM) and B41 (0101:K99:NM) adhered less intensively to isolated epithelial cells of older animals than of neonates. The results suggest that resistance of older animals to diarrheal disease caused by K99('+) ETEC may be partly due to resistance of adhesion. Nonencapsulated mutants of four K99('+) ETEC strains adhered in higher number than did the encapsulated parental strains. Both the encapsulated and nonencapsulated forms of ETEC strain 431 grown at 18(DEGREES)C (K99 production suppressed) adhered poorly to the isolated cells. A K99('-), non-ETEC strain adhered poorly in both encapsulated and nonencapsulated forms. The results indicated that K99 was the principal mediator of in vitro adhesion of the ETEC strains and that capsule impedes the in vitro adhesion. Experiments using infections with rotavirus and ETEC were designed to reproduce a syndrome of severe, watery, fatal diarrhea in gnotobiotic calves about 1 week old as has been reported to occur in calves with dual infections in natural conditions. Variables tested which did not result in fatal or severe diarrhea or which did not cause more severe disease in dually inoculated calves than in monoinoculated calves were: (1) feed increased to 2 times baseline, (2) dose of ETEC increased to 10 times baseline, (3) calves inoculated when 2 days old, (4) replacement of the ETEC strain with an E. coli that causes septicemia, and (5) use of a different strain of rotavirus. When the observation period was extended to 6 days, a severe, watery, fatal diarrhea occurred in 6 of 12 calves 32 to 72 hours after dual inoculation at 5 days of age. ETEC strain B44 tended to colonize the ileum of dually inoculated calves more intensively than it did ileum of monoinoculated calves. Additionally, there was significantly more severe atrophy of the ileal villi of dually inoculated calves. Those effects of the dual infections were consistent with synergistic interaction of the two infections.



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Copyright Owner

Paul Lewis Runnels



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214 pages