Serological characterisation of Actinobacillus pleuropneumoniae strains of serotypes 1, 9 and 11.

Various serological tests such as agglutination, coagglutination, indirect haemagglutination, immunodiffusion and counterimmunoelectrophoresis were used to characterise serologically Actinobacillus pleuropneumoniae isolates of serotypes 1, 9 and 11 using rabbit hyperimmune sera against serotypes 1 to 12. The rapid slide agglutination test using whole-cell suspension and the indirect haemagglutination test using whole-cell saline extract as antigens gave type specific reactions for serotypes 1 and 9. Antigens comprising saline extracts of boiled or autoclaved cells demonstrated common epitopes among the isolates of all three serotypes in the indirect haemagglutination test. Quantification of the type and group-specific antigens by the coagglutination test. Quantification of the type and group-specific antigens by the coagglutination test distinguished serotypes 1 and 9 strains from those of serotype 11. Results of absorption studies in immunodiffusion tests indicated that the cross-reactivity encountered among strains of serotypes 1, 9 and 11 might be due to common epitopes associated with cell-wall antigens. However, they certainly also have type-specific epitopes, possibly associated with superficially located, capsular antigens.