Enzyme-linked immunosorbent assay for Streptococcus agalactiae antibodies in bovine milk

An enzyme-linked immunosorbent assay (ELISA) for the detection of Streptococcus agalactiae antibodies in bovine milk was developed using whole bacterial cells as antigen. Microtitre wells were coated overnight at room temperature with a 1:64 dilution of antigen in 0.05M carbonate-bicarbonate buffer at pH 9.6. After washing, milk whey samples diluted 1:40 were added, incubated overnight and again washed. After incubation with rabbit antibovine serum, bound antibody was detected with alkaline phosphatase conjugated sheep antirabbit serum. Using the ELISA, the levels of Str agalactiae antibodies in the individual quarters of the mammary glands of cows in a severely infected dairy herd were measured. A high proportion of cows had specific antibody to Str agalactiae in one or more quarters. Using ELISA in association with electronic cell count and bacterial isolation, it was possible to identify latent and subclinical carriers of infection.