Final classification of Bisgaard taxon 9 as Actinobacillus arthritidis sp. nov. and recognition of a novel genomospecies for equine strains of Actinobacillus lignieresii.

The research aims at classifying Bisgaard taxon 9 under the new species Actinobacillus arthritidis, and introduces a new genomospecies for horse strains of Actinobacillus lignieresii based on their genetic and phenotypic differences.

Overview of the Study

• The study began with the identification of bacteria variant in diseased and healthy horses. There were 18 isolates categorized as Bisgaard taxon 9 and 11 as Actinobacillus lignieresii. Variations in the two sets were noted mainly in their alpha-galactosidase and raffinose fermentation traits.
• More specifically, all Bisgaard taxon 9 samples were alpha-galactosidase- and raffinose-positive but showed variations in their fermentation of (+)L-arabinose and (-)D-sorbitol. Actinobacillus lignieresii strains were found to be devoid of these characteristics except for raffinose.

Genetic Similarity and DNA Binding

• With regards to genetic similarities, two strains from the (-)D-sorbitol-negative group of taxon 9 exhibited a 16S rRNA similarity of 99.6%. In the (-)D-sorbitol-positive group, a 99.5% similarity was discovered between two strains.
• Upon performing DNA-DNA hybridization, two distinct strains from the (-)D-sorbitol-negative group showed 89% DNA binding. These strains were closely related to a strain of Actinobacillus lignieresii with a 64% similarity.
• For the (-)D-sorbitol-positive group, there was 83% DNA binding between two strains and a 76% binding with the (-)D-sorbitol-negative group.

Proposition for New Classifications

• Based on these results, the researchers proposed Actinobacillus arthritidis sp. nov. for 12 strains of the (-)D-sorbitol-positive group and Actinobacillus genomospecies 2 for the six strains of the (-)D-sorbitol-negative group.
• Phenotypically, these two proposed species differ in (-)D-sorbitol fermentation and can be separated from Actinobacillus equuli due to their negative reaction for trehalose, and a positive reaction for alpha-galactosidase places them apart from A. lignieresii.

Conclusion and Recommendations

• In the final analysis, the study suggests that the horse strains of A. lignieresii introduce a new genomospecies of Actinobacillus, attributing it to genomospecies 1. This is largely due to their lack of current phenotypic characteristics that could enable it to be separated from the main type strain of A. lignieresii.