Diversity among isolates of Actinobacillus equuli and related organisms as revealed by ribotyping.

This research investigation aimed to study the genetic diversity within Australian isolates of a kind of bacteria called Actinobacillus equuli by using a method called ribotyping. The results of the study indicate that A equuli is a diverse species, with different types of A equuli isolates exhibiting diverse characteristics.

Methods and Isolates

• The ribotyping, a genotypic method, was applied using the enzyme HaeIII to evaluate genetic diversity amongst 12 field isolates of A equuli with five being capable of fermenting L-arabinose, a type of sugar.
• One field isolate of Pasteurella caballi and two unidentifiable field isolates were also included in the study. The majority of these isolates were obtained from horses in Australia, with the exception of three isolates of A equuli procured from horses and a pig in Africa.
• In addition, the type strains for A equuli and P caballi and a reference strain for Bisgaard Taxon 9 were included in the study for comprehensive analysis.

Ribotype Analysis and Clustering

• The patterns observed from ribotyping were analysed by computerised cluster analysis. This led to the formation of five distinct clusters ranging from A to E.
• The L-arabinose positive A equuli were assigned to cluster A. The remaining seven A equuli isolates (all of which were L-arabinose negative) were grouped into cluster B along with the type strain.
• The unclassifiable isolates were distributed into clusters C and D. One unclassified isolate, along with the reference strain for Bisgaard Taxon 9, made up cluster C. The remaining unclassified isolate formed cluster D.
• Cluster E included the field isolate and the reference strain of P caballi.

Conclusions and Implications

• The results suggest that there are substantial diversity and distinct differences between L-arabinose positive and negative isolates of A equuli. Hence, A equuli is considered a diverse species.
• Another valuable finding from this study is that ribotyping could be beneficial in confirming the identity of A equuli-like organisms sourced from horses in field conditions.
• This genetic differentiation of isolates could prove significant for epidemiological studies and in understanding the pathogenicity and disease outcomes of different strains of A equuli and related species.