Is Rhodococcus equi a soil organism?

The research article aims to determine whether Rhodococcus equi is a soil organism, based on numerical taxonomic and ecological studies of 189 isolates of Rhodococcus equi and related organisms.

Numerical Taxonomic Study

• A total of 189 isolates of Rhodococcus equi and related organisms, as well as 16 marker strains representing Rhodococcus and Corynebacterium genera, were studied. These organisms were examined for 160 unit characters.
• Results of this numerical taxonomic study indicated that Rhodococcus equi forms a distinct and relatively homogeneous cluster. This suggests that it is different from other recognized species of Rhodococcus and Corynebacterium.

Ecological Considerations

• The research suggests that Rhodococcus equi falls into the Rhodococcus genus both taxonomically and ecologically. Other members of the Rhodococcus genus are known soil organisms.
• The idea that Rhodococcus equi could be a commensal in the gastrointestinal tract seems unlikely. This conclusion is based on the finding that, unlike gut commensals, Rhodococcus equi is an obligate aerobe, with an optimum temperature requirement of 28-30 degrees Celsius. It is also sensitive to bile salts and can utilize simple organic compounds as carbon or carbon-and-nitrogen sources.
• Evidence points to the fact that isolation of Rhodococcus equi from animals’ gut contents is dependent on the animals’ access to grazing. This further signifies its relation to the soil environment.

Conclusion

• Overall, the taxonomy and ecological data support the conclusion that Rhodococcus equi is a soil organism. Hence, the research provided valuable information in understanding the ecological background of Rhodococcus equi and its separation from other organisms.