Prevalence of virulent Rhodococcus equi in isolates from soil collected from two horse farms in South Africa and restriction fragment length polymorphisms of virulence plasmids in the isolates from infected foals, a dog and a monkey.

This research investigates the presence of virulent Rhodococcus equi, a harmful bacterium, in soil samples from two horse farms in South Africa and in clinical samples from various animals, including six foals, a dog, and a monkey.

Overview of the Study

• The researchers tested soil samples from two horse farms and clinical samples from various animals for the presence of Rhodococcus equi, a bacterium that can cause pneumonia in young foals.
• This bacterium can exist in virulent (disease-causing) and avirulent (non-disease causing) forms. The researchers wanted to see if there were differences in the prevalence of these forms in different environments.
• Additionally, the virulent isolates were also probed for the presence of specific virulence-associated antigens and virulance plasmids, genetic elements that contribute to their disease-causing capacity.

Key Findings

• Rhodococcus equi was found in almost all soil samples from both farms. The amount ranged from 5.0 x 10(1) to 3.3 x 10(4) colony forming units per gram of soil.
• The virulent form of R. equi was found in three soil samples from one farm (3.8% of the isolates from that farm), but not in any isolates from the other farm.
• In terms of virulence plasmids, one virulent R. equi isolate contained a type I, 85-kb plasmid, while the other two contained a type I, 87-kb plasmid.
• Of the nine clinical isolates (three from foals, one from a foal foetus, one from a dog, and one from a monkey), five from the foals showed virulent R. equi. These five isolates all expressed virulence-associated antigens, contained an 85-kb type I plasmid, and were taken from cases of pneumonia typical of R. equi infection.
• The remaining four clinical isolates (from the other foals, dog, and monkey) were avirulent R. equi.

Summary

• This study provides important insight into the prevalence and distribution of the virulent form of Rhodococcus equi on these horse farms in South Africa, its potential role in causing disease in a variety of hosts, and the genetic mechanisms by which it exerts its virulence.
• The findings also suggest potential exposure risks for horses and other animals in similar environments. Such research can potentially support measures to prevent and control infections in these settings.