Characterization of Pasteurella multocida from nasal cavities of piglets from farms with or without atrophic rhinitis.

A total of 137 strains of Pasteurella multocida isolated from the nasal tracts of pigs with and without clinical atrophic rhinitis (AR) were studied for their biochemical, antigenic, and toxigenic characteristics. There were no major biochemical differences among the P. multocida isolates. Capsular antigen types A and D were both present in the nasal cavities of the pigs with or without clinical AR. However, the prevalence of type D was higher on farms with pigs with AR. Types A and D with different somatic antigens could both be present in the same pig. There was no correlation between somatic types and/or capsular types with the clinical AR status of the pigs on the farm. Toxigenic isolates were found only in pigs which had a problem of clinical AR, and a great majority of these isolates belonged to type D. Since there was a high level of heterogeneity of the strains in the P. multocida population on a farm, several strains should be characterized before the diagnosis of AR could be excluded on the basis of the absence of isolation of rhinopathogenic P. multocida strains.