Characterization of the cattle serum antibody responses against TEM β-lactamase and the nonimmunogenic Escherichia coli heat-stable enterotoxin (STal)

In order to test the use of a subunit recombinant vaccine for its capacity to induce antibodies against the nonimmunogenic heat-stable enterotoxin STa from Escherichia coli and the TEM-1 β-lactamase, cattle were immunized with a hybrid protein created by insertion of the STa sequence at position 197 of the TEM-1 β-lactamase. Specific anti-STa IgG and IgG1 antibodies were detected at low levels, while no IgG2 antibodies were detected. In contrast, high levels of the different anti-TEM IgG subtypes were detected in cattle sera. In addition, β-lactamase activity was inhibited by the sera. The presence of antibodies against STa and TEM-1 β-lactamase was assessed in sera from 366 cattle taken from the field. No significant level of IgGs against the toxin or the TEM-1 was detected. A comparison of the antibody level between the immunized and the nonimmunized animals clearly demonstrated that STa was not able to induce a significant level of antibodies in the vaccinated animals. In contrast, a strong antibody response against TEM-1 β-lactamase was demonstrated.