Protective effects of antibody against intestinal invasion by Escherichia coli.

Seven Escherichia coli isolates from newborn calves with diarrhea were examined for enteropathogenic properties. One isolate penetrated into HeLa cells, four produced enterotoxin(s) and the remaining two possessed neither of these properties. Penetration of E. coli into HeLa cells was inhibited by antibody in bovine colostrum and in bovine and rabbit immune sera. The effective antibodies appeared to be mostly of the IgM class. The invasion by E. coli isolates was also examined by inoculation of the bacteria into the small intestine of E. coli-immunized and non-immunized guinea pigs. The isolate which penetrated into HeLa cells could penetrate the intestinal mucosa to be disseminated into various organs of non-immunized guinea pigs, but not of immunized guinea pigs, whereas no other isolates showed such pathogenicity in vivo. The inhibition of the invasion was observed when non-immunized guinea pigs were inoculated with the bacteria together with colostral or serum antibody. The results show the importance of antibody in the local defense mechanism against E. coli invasion.