Genetic diversity and associated pathology of Pasteurella multocida isolated from porcine pneumonia.

Pasteurella multocida is a widespread respiratory pathogen in pigs associated with atrophic rhinitis and contributing to aggravation of the pulmonary lesions. The aims of the present study were to characterize isolates of P. multocida from porcine bronchopneumonia by pulsed-field gel electrophoresis (PFGE), PCR based capsular typing and multilocus sequence typing (MLST) and to compare clonal complexes outlined with the type of histological lung lesions to investigate if a correlation between clonal lineages and lesions might exist. Isolates of P. multocida were obtained from cases of cranioventrally located porcine bronchopneumonia. All lung lesions were described and classified according to histological lesions. A total of 139 isolates, from lung (n=111), pericardial sac (n=21) and kidney (n=7) of 111 pigs were described using PFGE with ApaI as the restriction enzyme. Furthermore, 20 and 29 isolates were characterized by capsular serotyping and multilocus sequence typing, respectively. PFGE demonstrated 15 different clusters showing 50% or more similarity. All selected isolates were of capsular serotype A and only three main sequence types (ST) were detected among the isolates. Associations were not found between histopathology and clonal complexes of P. multocida. In conclusion, PFGE demonstrated a high diversity of genotypes of P. multocida associated with porcine bronchopneumonia. However, isolates obtained mainly belonged to few STs, indicating that isolates of P. multocida associated with porcine bronchopneumonia originates from a limited number of clonal lineages and therefore might have adapted to porcine hosts. No correlation was demonstrated between genotypes and types of lesions, and extra-pulmonary spreading was only rarely demonstrated.