Serologic detection of Actinobacillus pleuropneumoniae in swine by capsular polysaccharide-biotin-streptavidin enzyme-linked immunosorbent assay

Serologic detection of. Actinobacillus pleuropneumoniae infections in swine have been problematic due to antigenic cross-reactivity of Aps toxins, lip opolysaccharide, and outer membrane proteins between A. pleuro-pneumoniae s erotypes and other bacterial species. To maximize serologic specificity and sensitivity, we developed an assay that uses highly purified ii, pleuropne umoniae capsular polysaccharide (CP) conjugated to biotin, which is then bo und to streptavidin-coated enzyme-linked immunosorbent assay (CP-BS-ELISA) plates. This assay was used to test a panel of 240 serum samples from pigs prior to challenge, after challenge with bacterial species other than A. pl europneumoniac, or after challenge with A. pleuropneumoniae serotype 1, 5, or 7, Overall assay results for the individual sera tested were reproducibl e on the same day and on separate days. The sensitivity of the assay was 10 0% by ELISAs with biotin-CPs of serotypes I and 7 and 87.5% by ELISAs with biotin-CP of serotype 5. Specificity was 100% by ELISAs with biotin-CPs of serotypes 1 and 5 and 94.5% by ELISAs with biotin-CP of serotype 7, The bio tin-CPs of at least three A. pleuropneumoniae serotypes could be combined f or use in a screening assay to detect antibodies to CPs from strains of dif ferent serotypes, In conclusion, the CP-BS-ELISA proved to be a serotype-sp ecific and species-specific assay with high sensitivity for the identificat ion of pigs exposed to A. pleuropneumonia.