The effect of antisera on porcine enteropathogenic Escherichia coli in ligated segments of pig intestine.

Nineteen antisera produced in pigs against 14 enteropathogenic and five nonenterotoxigenic porcine strains of Escherichia coli were tested for their ability to inhibit gut loop fluid accumulation induced by homologous and heterologous organisms. In addition, four antisera produced in pigs by an intensive series of intravenous inoculations and three by a less intensive series of intramuscular injections of a polyvalent E. coli vaccine were evaluated. Antisera were also produced in rabbits against eight strains of porcine enteropathogens and tested in pig gut loops. Fluid inhibiting activity was detected in prevaccinal sera of pigs but not of rabbits. This activity was significantly increased following immunization. When single strains of E. coli were used for immunization the activity of the antisera against heterologous organisms varied considerably from one test strain to another and was usually much less than that against the homologous organism. The activity against heterologous organisms could not be associated with relatedness of the O, K and H antigens of the vaccine and the test strains. Antisera produced against a vaccine made by combining three strains were shown to exert inhibitory effects on heterologous organisms similar to those against homologous organisms. Considerably less activity against homologous and heterologous organisms was present in antisera produced by the series of intramuscular compared with the series of intravenous injections.