Capsular polysaccharide antigens for detection of serotype-specific antibodies to Actinobacillus pleuropneumoniae.

Capsular polysaccharides (CPS) of serotypes 1, 2, 5 and 7 of Actinobacillus (Haemophilus) pleuropneumoniae were obtained from 18 h culture supernatants by precipitation with hexadecyltrimethyl-ammonium bromide (Cetavlon) followed by extraction with sodium chloride and reprecipitation in ethanol. These crude extracts, and portions purified further by phenol extraction to remove contaminating proteins, were evaluated as antigens for the detection of serotype-specific antibodies to A. pleuropneumoniae in sera from immunized rabbits and swine by an enzyme-linked immunosorbent assay. The crude extracts reacted strongly with homologous antisera, but except for serotype 1 showed considerable cross-reactivity with antisera to other serotypes. Phenol extraction greatly improved the serospecificity of the antigens from serotypes 1, 7 and, to a lesser extent, 5. The serotype 2 CPS antigen showed poor reactivity following phenol extraction, and did not appear as useful for detection of serotype-specific antibodies.