Molecular diversity of porcine and human isolates of Pasteurella multocida

Aims:  To examine the variability among Pasteurella multocida strains isolated from pigs (nasal, tonsil and lung specimens) and humans in France. Methods and Results:  The genetic diversity of 117 French isolates of P. multocida, obtained from pigs (n = 101) and humans (n = 16) and three reference strains, was evaluated by pulsed-field gel electrophoresis (PFGE) after macrorestriction with ApaI. Sixty-four patterns were detected. The genetic relationships revealed five clusters (Aa1, Aa2, Aa3, Ab and B). The pig isolates obtained from pneumonic lungs and nasal cavities were clustered in groups Ab and Aa1, respectively (P < 0·05). Up to four different PFGE patterns were detected in the same farm. Isolates producing dermonecrotic toxins were clustered only in group Aa1, suggesting that the toxigenic isolates were more genetically homogenous than the others. Conversely, cluster Aa3 was significantly associated with human isolates even if the human isolates are spread over most of the clusters. Conclusions: Pasteurella multocida strains were genetically diverse, but pig and human isolates were significantly clustered in distinct phylogenetic groups. Significance and Impact of the Study:  The discrimination index was >0·95 in both populations of human and pig isolates. Therefore, ApaI-PFGE seems to be a useful tool for epidemiological tracing of P. multocida infections.