Simple visual assay for determination of Pasteurella haemolytica cytotoxin neutralizing antibody titers in cattle sera.

A simple visual assay is described for determining the capacity of bovine serum to neutralize the cytotoxin produced by Pasteurella haemolytica serotype 1. The test was reproducible from day to day with different target cell populations and cytotoxin preparations. Cytotoxin neutralization titers obtained by the visual assay were comparable to those determined by the trypan blue exclusion and 51Cr-release methods. The visual assay was used to measure neutralization titers of bovine sera obtained from vaccination experiments and fractions of purified serum obtained by gel filtration. The major advantages of the visual assay over other assays are that it is rapid, inexpensive, and does not use radioisotopes. It also does not require specialized equipment, making it adaptable to most laboratories.