Actinobacillus suis-like organisms and evidence of hemolytic strains of Actinobacillus lignieresii in horses.

The study encompasses an investigation into the Actinobacillus suis-like organisms present in horses and a llama, including a particular focus on potential hemolytic strains of Actinobacillus lignieresii. The researchers used cultural characteristics, enzyme profiles, carbohydrate fermentation, and polyacrylamide gel electrophoresis to analyse both local isolates and referential strains. The results suggested that some of the strains were indeed hemolytic variants of A lignieresii, and showed various differences in biochemical characteristics and enzyme activity.

Research methodology

• The researchers examined 37 local isolates of Actinobacillus suis-like organisms (ASLO) from both diseased and clinically normal horses, as well as from a llama.
• These were then compared with reference strains of multiple Actinobacillus species for their cultural characteristics, carbohydrate fermentation, and enzyme profiles.
• This comparison was further extended with the use of whole-cell protein polyacrylamide gel electrophoresis.
• Carbohydrate fermentation was categorized using an API-CH gallery, leading to the subdivision of the equine ASLO isolates into 6 API-CH biotypes. The llama isolate represented a unique biotype.

Main findings

• The biochemical comparisons between A suis and ASLO didn’t show any significant or consistent differences.
• Enzyme analysis revealed the existence of 5 API-ZYM biotypes, including one that consisted of 4 esculin-negative ASLO cultures and the reference strain of A lignieresii.
• The researchers concluded that these 4 strains were likely hemolytic variants of A lignieresii based on these findings.
• Protein electrophoresis revealed 15 banding patterns, 10 of them were equine ASLO strains. The reference strains of A suis were found to predominantly share a pattern with equine ASLO.
• Some of the Actinobacillus species had unique profiles, while others showed similar characteristics.

Significance of research

• The comparison between the different testing methods and a vague relation to the anatomic source of the strains illuminates the complexity of the Actinobacillus species, their similarities and their differences.
• Further study into the differences observed could provide more targeted treatment and prevention strategies for diseases caused by these bacteria in horses and other animals.