[Contribution to the differentiation of haemophilus-strains isolated from chickens. II: Serological examinations using the plate-agglutination test].

A total of 31 field isolates, 23 of them belonging to the H. paragallinarum species were examined serologically by means of the rapid slide agglutination test (RSA-test). One H. paragallinarum strain of serotype A, one of serotype B, and one serologically unclassified strain from California were used as reference strains. In addition, one strain of H. parainfluenzae was 'included 'in these studies. On the basis of the results of the RSA-tests With rabbit antisera 2 distinct serotypes of H. paragallinarum were differentiated. Cross reactions were observed among the serotypes which could be eliminated by dilution and absorption of the antisera. Eight of 23 H. paragallinarum isolates belonged to serotype A and 13 to serotype B. Two isolates showed spontaneous agglutination in 0.85% saline. Seven of 8 other isolates of Haemophilus bacteria, representing a culturally and biochemically separate group, could be distinguished from H. paragallinarum strains without difficulty. One strain showed spontaneous agglutination. The other 7 isolates formed 4 distinct serotypes on the basis of the RSA-tests, of which 3 isolates belonged to serotype 1, 2 to serotype 2, and one each to serotypes 3 and 4. Weak cross reactions were observed among these serotypes. No strains isolated from chickens included in this study were serologically identical with the strain of H. parainfluenzae.