Actinobacillus suis-like organisms in horses.

The research article explores the existence and properties of Actinobacillus suis-like organisms in horses, which have been identified in the University of California Veterinary Medical Teaching Hospital as early as 1975. The paper also examines the organisms’ sensitivity to therapeutic medications.

Recognition of Actinobacillus suis-like organisms

• These organisms have been known to exist in equines since 1975, with the most common source being transtracheal washings (65% of cases).
• They are gram-negative, meaning they don’t retain a certain dye in Gram staining, a method used to differentiate bacterial species into two large groups. This gives insight into their cell wall composition and can indicate possible treatment strategies

Characteristics of Actinobacillus suis-like organisms

• These bacteria produce hemolysis on blood agar, meaning they destroy red blood cells, causing them to release their hemoglobin into the surrounding medium.
• The organisms have multiple positive reactions for oxidase, urease, o-nitrophenyl-beta-D-galactopyranoside, and esculin. These are all enzymes or compounds that they metabolize or produce, which provide more insight into the physiological characteristics of the bacterium.
• Carbohydrate reactions of these bacteria were variable, indicating different strands of the same species can have different nutrient utilization patterns.

Sensitivity to Therapeutic Medications

• The study found that the Actinobacillus suis-like organisms were 90% sensitive to therapeutic concentrations of several antibiotics including amikacin, cephalothin, chloramphenicol, gentamicin, kanamycin, tetracycline, and trimethoprim-sulfamethoxazole. This implies these medications may be effective treatment options against infections caused by these organisms.

Co-existence with Other Bacteria

• The study also noted that other aerobic and anaerobic bacteria are often recovered alongside the Actinobacillus suis-like organisms. This can mean that these organisms often live in polymicrobial environments or cause co-infections along with other bacteria.