Serologic studies on porcine strains of Haemophilus parahaemolyticus (pleuropneumoniae): agglutination reactions.

Fifteen strains of Haemophilus parahaemolyticus (pleuropneumoniae) represented by 6 American isolates, 6 Swedish isolates, and 3 reference strains of Nicolet's serotype 1, 2 and 3, were used in serologic studies by agglutination and agglutinin-adsorption tests. By whole cell-agglutination tests in rabbit antiserums, 3 additional serotypes, 4, 5, and 6, were identified. All strains had strong serotype-specific agglutinating properties. Occasional weak cross reactions could be eliminated by appropriate adsorptions without effect upon type-specific reactivity. The Swedish isolates were assigned to serotypes 2, 3, 4, and 6, and the American isolates, to serotypes 4 and 5. All European isolates were distinct from 5 of the 6 American strains. An American culture isolated from a steer and another from a lamb were identical in their agglutination reactions with the porcine isolates of serotype 5. The serotyping of isolated strains is important in the epizootiologic and immunologic studies of H parahaemolyticus infections.