Enzyme-linked immunosorbent assay for detection of serum antibodies to Pasteurella haemolytica cytotoxin (leukotoxin) in cattle.

An enzyme-linked immunosorbent assay (ELISA) was developed for detection of bovine serum antibodies to the cytotoxin (leukotoxin) of Pasteurella haemolytica. A partially purified, cytotoxic, and immunogenic protein obtained from supernatants of logarithmic-phase P. haemolytica was used as the ELISA antigen. Preadsorption of sera with various cytotoxic, somatic, and capsular antigen preparations demonstrated that the assay was specific for anticytotoxin antibodies. ELISA anticytotoxin titers had a strong, significant correlation to cytotoxin-neutralizing-antibody titers. The ELISA, however, was more rapid and allowed for greater numbers of samples to be run than did the neutralization technique. ELISA anticytotoxin titers were high in cattle vaccinated with a live P. haemolytica vaccine, whereas unvaccinated cattle and cattle receiving a P. haemolytica bacterin had low ELISA anticytotoxin titers. A significant positive correlation between ELISA titers and resistance to experimental bovine pneumonic pasteurellosis was present.