A bacteriological and serological study of experimental escherichia coli infection of calves.

Twelve hundred bacterial cultures from thirty newborn calves were examined serologically to determine the experimental pathogenicity of E. coli serotypes as well as the influence of enteric bacteria naturally present in the calves. Serotype O115:K.:H18 was pathogenic, O9:K35:H1O was not, and unclassified E. coli OX28 was questionable. Klebsiella sp. and E. coli OX28 occurred naturally in the calves and was responsible for some mortality. Contact exposure in two groups of calves was not successful. All calves had a detectable gamma-globulin level whether or not they had nursed the dam. Antibody to four E. coli O groups was present at a gamma-globulin level above 0.78 gm% but not belw 0.60 gm%. Antibody was associated with survival of calves given E. coli serotype 115:K.:H18 but not the less virulent 9:K35:H1O. There was no correlation between antibody level and bactericidal activity of the serums. The latter did not appear to offer resistance to infection by itself, but antibody level and bactericidal activity to E. coli O115 and O78 did protect all calves experimentally infected with different serotypes.