Evaluation of a LPS-based glycoconjugate vaccine against bovine Escherichia coli mastitis: Formation of LPS Abs in cows after immunization with E. coli core oligosaccharides conjugated to hemocyanine.

The immune response of cows against the core oligosaccharide of Escherichia coli rough mutants (core types R1-R4, K-12 and J-5) was investigated after immunization with a synthetic glycoconjugate composed of deacylated LPS conjugated to hemocyanine (22 animals). Ab formation was measured by ELISA using LPS or deacylated LPS conjugated to BSA as an Ag. The glycoconjugate immunogens were used to vaccinate cows (36 animals), which were then challenged intramammarily with E. coli O 157 (K1 negative, R1 core type). Compared with control groups no protection was observed, although high titers against the R1 core type were detected in vaccinated animals. Western blots using the immune sera showed that the Ab response was directed against the core region and not against the O-antigen, which may explain the failure of the vaccine.