Characterisation of Australian isolates of Actinobacillus capsulatus, Actinobacillus equuli, Pasteurella caballi and Bisgaard Taxa 9 and 11.

The study sought to identify and characterise 16 bacterial strains that had been previously identified as Actinobacillus equuli in Australian animals, primarily horses, but found that only nine were actually A equuli. It also discovered for the first time that A capsulatus, P caballi and Bisgaard Taxa 9 and 11 were present in Australia.

Objective and Methods

• The study aimed to conduct an in-depth phenotypic characterisation of 16 bacterial isolates that had been initially categorised as Actinobacillus equuli.
• The bacterial isolates came from Australian animals: 15 were taken from horses, and one was obtained from a rabbit.
• To attain a comprehensive comparison, these isolates were compared with reference strains of not only A equuli but also several other species including A capsulatus, Pasteurella caballi and Bisgaard Taxa 9 and 11.

Results & Findings

• The examination revealed that only nine of the sixteen isolates were Actinobacillus equuli.
• The isolate obtained from the rabbit was identified as A capsulatus, and an isolate from the horses turned out to be P caballi.
• There were two isolates that belonged to Bisgaard Taxon 11, and one that was part of Bisgaard Taxon 9.
• Interestingly, two isolates could not be grouped under any of the recognised species or taxa, indicating the potential presence of unknown bacterial strains.

Conclusions

• This research emphasizes the critical nature of full characterisation of Actinobacillus-like organisms isolated from horses and rabbits, suggesting that mere classification based on initial observation may lead to inaccurate identification.
• The significant finding of this study is the first-ever recognition of A capsulatus, P caballi, and Bisgaard Taxa 9 and 11 in Australian fauna, expanding the known biogeographical range of these bacterial species.