Serological Characterization of Haemophilus Pleuropneumoniae (Actinobacillus Pleuropneumoniae) Strains and Proposal of a New Serotype: Serotype 9

Abstract

Ten strains of H. pleuropneumoniae isolated from 10 herd outbreaks of pleuropneumonia were studied by means of the slide agglutination test, the indirect haemaggluitiniation (IHA) test and by gel diffusion. The strains were antigenically homogeneous and serologically distinct from serotypes 1 through 8. It is therefore proposed to refer these strains to a new serotype: serotype 9, with strain CVJ 13261 as the type strain.

In addition to the serotype-specific capsular antigens, capsular antigen of serotype 1 (strain 4074) could be demonstrated in the 10 strains by means of gel diffusion analyses.

In cross protection studies it was shown that the antigenic determinants shared by serotypes 9 and 1 were unable to yield a sufficient protection against disease. Thus, parenteral immunization with a killed 6-h culture of serotype 9 did not afford an acceptable protection against challenge with serotype 1 since only 3 of the 5 vaccinates were protected. The reverse experiment showed that parenteral immunization with serotype 1 only protected 1 out of 4 vaccinates.

Sammendrag

Ti Haemophilus pleuropneumoniae stammer, isoleret fra hollandske besætningsudbrud af pleuropneumoni blev undersøgt serologisk ved hjælp af objektglasagglutination, indirekte haemagglutination (IHA) og gel diffusion.

De 10 stammer udgjorde en homogen gruppe i antigen henseende og var serologisk forskellige fra de hidtil kendte serotyper 1 til 8. Gruppen er derfor blevet identificeret som en ny serotype: serotype 9 med stamme GVJ 13261 som typestamme.

Ved hjælp af gel diffusion blev det påvist, at de 10 stammer, foruden serotype specifikke kapselainitigener, også indeholdt kapselantigener af serotype 1 (stamme 4074).

Krydsimmuniseringsforsøg viste, at en dræbt kultur af H. pleuro-pneumoniae serotype 9 kun beskyttede 3 af 5 vaccinerede grise mod challenge med serotype 1. Efter vaccination med en dræbt kultur af serotype 1 var kun 1 af 4 grise beskyttede mod challenge med serotype 9. Disse resultater viser, at de antigene determinanter, der er fælles for serotype 1 og 9, ikke aleme er i stand til at give en tilstrækkelig beskyttelse mod pleuropneumoni.