Virulent Rhodococcus equi is an important pathogen in foals aged 1 to 3 months, but its incidence in Tennessee, U. S. A., is poorly understood. Ten soil samples were collected from a Tennessee walking horse farm in Tennessee. The presence of R. equi was investigated and 107 isolates were tested for the presence of 15- to 17-kDa antigens (VapA) by immunoblotting and PCR. R. equi was isolated (103-104 colony forming units/g) from 8 of the 10 soil samples. Twenty-four VapA-positive isolates were detected from 7 of the 8 culture-positive samples with a prevalences ranging from 6.7 to 50%. Of the 24 virulent isolates, 21 contained an 85-kb type I plasmid, and 3 contained an 85-kb type III plasmid which had been uniquely isolated from soil isolates in Texas. There was no evidence of R. equi infection on the farm, but the virulent form was widespread in the soil environment of the farm.
