Serological differentiation between infected and vaccinated cattle by visual and quantitative immunofluorescence using Brucella abortus antigen coupled sepharose beads.

The ability to differentiate cattle infected with brucellosis from animals vaccinated against the disease is of considerable economic advantage in countries adopting eradication schemes. Current serological tests such as bacterial tube agglutination do not readily distinguish cattle in this way. An immunofluorescent procedure was investigated in an attempt to overcome this problem. Antigenic extract of brucella abortus strain 544/W were coupled to sodium metaperiodate oxidised Sepharose CL4B beads. Following coupling, the beads were chemically reduced or blocked with rhodamine labelled BSA prior to reduction. Characterised bovine serum samples were tested by indirect immunofluorescence on both types of bead and by standard bacterial tube agglutination. Serological discrimination between infected and vaccinated cattle was achieved by fluorescence quantitation using unblocked beads and by visual determination of colour using rhodamine-albumin blocked beads. Bacterial tube agglutination failed to distinguish between the two groups of sera.