Epidemiologic study of results of pulsed-field gel electrophoresis of isolates of Rhodococcus equi obtained from horses and horse farms.

The research study explores the genetic variation among Rhodococcus equi isolates from horses and horse farms across different geographic regions, utilizing pulsed-field gel electrophoresis (PFGE). The findings indicate significant genetic diversity among the isolates with little correlation to their geographic or virulence status.

Research Methodology

• The research drew upon 290 isolates of Rhodococcus equi, of which 218 were virulent isolated from foals and 72 were avirulent collected from feces, soil, and respiratory tract samples.
• The isolates were gathered between 1985 and 2000 from horse samples and various horse farms in four different countries.
• The DNA from these isolates was digested with the restriction enzyme Asel and tested via pulsed-field gel electrophoresis (PFGE).
• The PFGE products were analyzed for similarities in banding patterns using dendrograms.
• A similarity matrix was created for the isolates, which was then checked for nonrandom distributions of similarity values in relation to groupings of interest (like geographic region, virulence status, etc.).

Research Findings

• The analysis found little correlation between the genetic profile (based on PFGE) of the isolates and their geographic source, virulence status, or specific region within Texas.
• Generally, the isolates of R. equi were less than 80% similar based on PFGE analysis.
• Rarely, isolates from the same farm were of the same strain, indicating a high level of genetic diversity.

Research Conclusions

• Significant chromosomal variability is observed among R. equi isolates from the same farm, sites within Texas, or among different countries.
• Infections could rarely be linked with a specific site or geographic region based on PFGE analysis.
• This study challenges the assumption that R. equi isolates from the same farm or geographic region are genetically similar, suggesting a complex and diverse genetic backdrop for these organisms.

This research, therefore, presents useful insights into the genetic diversity of R. equi isolates across varying geographic and environmental contexts, which may have implications for infection tracking and control strategies.