Actinobacillus and Pasteurella species isolated from horses with lower airway disease

Seventy-three bacterial isolates from 65 horses with and without evidence of lower airway disease were identified to assess whether the association with disease was accounted for by a small or large number of species. Just over half (50.5 per cent were Actinobacillus equuli, 17.8 per cent were A suis-like, 11 per cent were Pasteurella pneumotropica, 8.2 per cent were A lignieresii, 6.8 per cent were P haemolytica and 5.5 per cent were P mairii. These results suggest that a range of Actinobacillus and Pasteurella species can be isolated from the lower airways of horses, with many of the isolates being A equuli. Among the horses examined, lower airway inflammation was significantly associated with A suis-like bacteria and A lignieresii. However, these two species constituted too small a proportion of the undifferentiated Actinobacillus/Pasteurella species to explain the association of this group of bacteria with lower airway disease. Since A equuli constituted just over 50 per cent of the group of bacteria it is possible that it too is playing a significant role in lower airway disease.