Serological classification of Haemophilus paragallinarum with a hemagglutinin system.

Antigens, prepared from 17 strains of Haemophilus paragallinarum by treatment with potassium thiocyanate followed by sonication, uniformly agglutinated glutaraldehyde-fixed chicken erythrocytes and formed specific hemagglutination inhibition antibodies in rabbits. Attempts were made to classify the strains into serotypes by a combination of cross-hemagglutination inhibition and cross-absorption tests, using the hemagglutinating antigens, designated as HA-L hemagglutinin, and their antisera. The cross-hemagglutination inhibition tests showed the existence of three distinct groups among the 17 strains. Further cross-absorption studies indicated that two of the three groups could be subdivided into three serotypes each, forming a total of seven serotypes, designated HA-1 through HA-7. Classification based on the serotype-specific HA-L system was found to be superior in its wider and more clearly defined specificities to other previous classifications, which are based on the agglutination test. There appeared to be a correlation between serotypes and geographic origins of the strains.