Variability of Pasteurella multocida isolated from Icelandic sheep and detection of their toxA gene

Pasteurella multocida can be part of the upper respiratory flora of animals, but under conditions

of stress or immunocompromisation, the bacteria can cause severe respiratory symptoms. In this

study, we compared 10 P. multocida isolates from Icelandic sheep with respiratory symptoms

and 19 isolates from apparently healthy abattoir sheep. We examined capsule type, genetic

variability and the presence of the toxA gene in the two groups. Surprisingly, we found that all

ovine P. multocida isolates examined in this study carried the toxA gene, which markedly differs

from what has been published from other studies. Interestingly, all isolates from abattoir animals

were capsule type D, whilst bacteria isolated from animals with clinical respiratory symptoms had

capsule type A, D or F. Examination of seven housekeeping genes indicated that the clinical

respiratory isolates were significantly more heterogeneous than the abattoir isolates (P<0.05,

two-tailed Mann–Whitney U test). The results suggest that there may be at least two groups of

P. multocida in sheep – a genetically homogeneous group that resides in the respiratory tract

and a genetically heterogeneous group that is the predominant cause of disease.