Prevalence of virulent Rhodococcus equi in soil from five R. equi-endemic horse-breeding farms and restriction fragment length polymorphisms of virulence plasmids in isolates from soil and infected foals in Texas.

The study investigates the occurrence and genetic diversity of a particular bacteria known as Rhodococcus equi in soil samples from five horse-breeding farms in Texas that were experiencing outbreaks. The research also considers samples from 100 infected foals in the same area and uses tests to identify particular proteins and plasmids connected to the bacteria’s harmfulness.

Research Methodology

• The researchers obtained 462 Rhodococcus equi isolates from 64 soil samples gathered on five horse-breeding farms known for R. equi outbreaks. In addition, they studied isolates from 100 infected foals from the same region.
• The team checked these isolates for a 15-17-kDa virulence-associated protein antigen (VapA) and virulence-associated plasmids by performing immunoblotting and polymerase chain reaction (PCR) tests.
• Isolated plasmid DNAs were subject during microbiological analyses to a process known as digestion with restriction endonucleases. This method helps to calculate the size of the plasmids and facilitates comparison of polymorphisms, which are variations at a specific location within the DNA.

Research Findings

• Rhodococcus equi was identified in the soil collected from all five farms. However, harmful R. equi was only found in three of those farms, forming 18.8% (87 of 462) of the total isolates.
• Of the 87 virulent soil isolates, varying quantities of different types of plasmids were found. These included an 85-kb type I plasmid, an 87-kb type I plasmid, a newly identified 85-kb type III plasmid (Tx 43), and a new 85-kb type IV plasmid (Tx 47).
• From the isolates obtained from infected foals, 96 were found to be virulent. These also contained varying quantities of the four different types of plasmids.
• The study discovered that there are at least four distinct R. equi virulence-associated plasmids in Texas, two of which were novel findings.

Conclusions From The Study

• Based on the virulence plasmid typing, there is a substantial geographic diversity in the R. equi isolates from clinical and environmental samples taken from the horse-breeding farms in Texas.
• The study also found that there wasn’t a strong correlation between the presence of virulent R. equi in farm soils and the R. equi disease status of those farms, suggesting that just the presence of these bacteria isn’t a clear disease indicator.