Haemophilus pleuropneumoniae serotyping.

A total of 126 Haemophilus strains isolated from porcine pneumonia were serotyped, using the indirect fluorescent-antibody technique. Of these, 103 were successfully typed within the recognized scheme of serotypes 1 to 5. Eleven strains were antigenically similar but were different from other strains of H. pleuropneumoniae or H. parasuis. These strains are proposed as serotype 7. Eight strains were not identified as serotype 1 when serum against strain Shope 4074 was used, but their identity as type 1 strains was concluded on the basis of complete cross-titrations, using unabsorbed and absorbed sera and indirect fluorescent-antibody and agglutination tests. The type-specific antigen of these strains may have been masked by an additional antigen. A similar situation was believed to exist for four strains which belonged to serotype 5 but did not react with serum against strain K17 (reference strain) in the indirect fluorescent-antibody test. Strain Femø was antigenically different from other H. pleuropneumoniae or H. parasuis strains and was proposed as serotype 6, thus replacing the "minor group" (represented by strain 202), which is of uncertain taxonomical status within the genus Haemophilus.