Rhodococcus equi in the soil environment of horses in Inner Mongolia, China.

The article focused on studying the distribution of Rhodococcus equi, a type of bacteria, in the soil where horses live in specific areas of Inner Mongolia, China. It concluded that the presence of this bacteria was significantly different depending on the areas and the pasturing systems practiced there.

Introduction and Methods

• The study was focused on the distribution of Rhodococcus equi – a bacterium which can cause lung infections in foals, in the soil of horse farms in Inner Mongolia, China. The researchers were interested in this topic as there were limited studies available on it.
• The team collected a total of 108 soil samples from native horse farms across different regions in Inner Mongolia, specifically the Hulun Beier and Xilin Goler grasslands, and Tongliao City. Various isolation methods were used to isolate R. equi from the collected soil samples. The isolated bacteria were then counted to gather information on their prevalence.

Findings

• Isolation rates of R. equi from soil samples varied significantly between the locations. The rates ranged from 25.9% to 30.0% in the grassland areas of Hulun Beier and Xilin Goler, whereas, in Tongliao City, the rate was substantially higher at 82.3%.
• Not only was the isolation rate higher, but the mean number of bacteria in the soil from Tongliao City was also 10 times more than those from the grasslands.

PCR Analysis and Identification of Virulence-Associated Proteins

• The isolated bacteria were examined using Polymerase Chain Reaction (PCR) for the presence of specific genes encoding virulence-associated 15-17 kDa antigen protein (VapA) and the 20 kDa antigen protein (VapB). These two proteins are associated with the disease-causing potential of the bacteria.
• However, none of the bacterial strains isolated were found to possess these virulence-associated proteins, indicating that they were not disease-causing, or ‘avirulent.’

Plasmid Profile Analysis

• The avirulent strains of R. equi were further examined for their plasmid profiles. Plasmids are small pieces of DNA that are separate from the bacterial chromosome and can carry additional genetic information. The presence of certain plasmids can contribute to the virulence of a bacteria, its antibiotic resistance, etc.
• The plasmid analysis showed that cryptic plasmids of various sizes were present in the bacteria, with an incidence rate of 13.3% to 21.5%.

Contrasting Results and Conclusions

• The findings of this study were contrasted with a previous study conducted by the same team in Ulaanbaatar, Mongolia, where they did not find any presence of R. equi in Mongolian horses.
• The researchers suggested that this difference in results might be attributed to the different pasturing systems practiced in Mongolia and Inner Mongolia, with Mongolia using a mobile pasturing system and Inner Mongolia working with a non-mobile pasturing system.