Determination of antibodies to Streptococcus agalactiae in the milk of dairy cows using the ELISA test

A sensitive 4-layers ELISA test for determination of antibodies against the pathogens of Streptococcus agalactiae in cows' milk was used for diagnosis of mastitis, with the aim to broaden these methods. Antigen was linked on the solid phase in the form of the whole bacteria, and milk was tested, diluted in the ratio of 1:10. Antigen bound-specific antibodies were labelled with pig antibodies against bovine immunoglobulins and in the next layer with rabbit antibody conjugated with peroxidases against pig immunoglobulins. After test visualisation and reading on the photometre, the results were given in the positivity per cent as a 100-multiple of the proportion of absorbance of the unknown sample and the positive control after subtraction of the negative control. Milk was examined in 36 dairy cows from three various breeding herds by that method. The samples were parallelly examined bacteriologically and cytologically. In the milk of dairy cows with positive S. agalactiae finding, the main level of antibodies expressed a positivity per cent, was 15.0%, while in bacteriologically negative animals it was only 6.2%. The dairy cows were divided into 8 groups, characterizing various stages of mastitis, according to the results of the individual treatments.