Optimalization of the detection of NAD dependent Pasteurellaceae from the respiratory tract of slaughterhouse pigs.

NAD dependent members of the family Pasteurellaceae were cultured from the nasal cavity, surface and cut surface of the tonsils, and from the apical and caudal lobes of the lungs of 303 slaughterhouse pigs from 5 different herds in order to obtain information on the ecology of these bacteria. The specimens were plated on two different selective agar media using a special dilution technique that resulted in a good separation of individual colonies. Bacteriological results were compared with serological and pathological findings. The bacteriological examination demonstrated that NAD dependent Pasteurellaceae belonging to the taxa previously described could be isolated from the surface and cut surface of the tonsils, and from lungs with and without gross pathologic lesions. Haemophilus parasuis was detected mainly from the nasal cavity, and Actinobacillus pleuropneumoniae mainly from the surface and cut surface of the tonsils (42%). From two herds, 19% and 24% respectively of the animals without antibodies against A. pleuropneumoniae serotypes 1 and 2 harboured the bacteria mainly in the tonsils. This may reflect a very recent infection or may suggest that A. pleuropneumoniae can colonize the tonsils without inducing a serologic reaction. Serological and bacteriological evidence of more than one serotype in the same herd indicates that natural infection with one serotype does not necessarily protect against another.