Enzyme-linked immunosorbent assay for detection of milk immunoglobulins to leukocidin toxin of Staphylococcus aureus.

Leukocidin toxin from a bovine strain of Staphylococcus aureus was partially purified by ion exchange chromatography. An enzyme-linked immunosorbent assay was developed to quantitate antibodies specific for leukocidin in bovine milk. This was used to assay quarter samples from 88 cows in a S aureus-infected herd for antibody levels to the toxin. Milk samples from 65 cows with S aureus infections in at least one quarter produced a mean optical density of 1.054, whereas milk samples from 23 cows that were free of bacteria on cultural examination had a mean optical density of 0.584. There was a significant difference (P less than 0.001) in milk anti-leukocidin levels between these 2 groups. Evaluation of serum samples from 40 of these cows indicated that the milk anti-leukocidin concentrations were reflective of systemic anti-leukocidin values. The capability of 57 milk samples to neutralize the cytolytic effect of minimal amounts of leukocidin on bovine peripheral blood neutrophils was examined. Good correlation existed between the enzyme-linked immunosorbent assay antibody concentration and toxin-neutralizing capability of individual milk samples.