Genotypic Characterization of Virulent Rhodococcus equi Isolated from the Environment of Hokkaido Native Horses in Hakodate, Hokkaido

Abstract

Rhodococcus equi was isolated from soil samples obtained from seven Hokkaido native horse farms in Hakodate, Hokkaido. R. equi was prevalent in all 59 soil samples collected from the seven farms at concentrations of between 7.5 × 102 and 7.5 × 104 colony-forming units per gram of soil. The isolates were examined for presence of the gene that encodes the virulence-associated 15-17 kDa antigen protein, VapA, using PCR. VapA-positive R. equi was isolated from 1-6% of isolates from three of the farms. This represents 1.4% of isolates from all farms examined (8 out of 590). The eight virulent isolates were characterized by plasmid profiling, restriction fragment length polymorphism analysis, and pulsed-field gel electrophoresis. All of the virulent isolates contained an 87-kb type II plasmid, but there were eight distinct VspI profiles. These results suggest that, although the Hokkaido horses of Hakodate are exposed to a variety of distinct types of virulent R. equi, the incidence of exposure is low or zero. An 87-kb type II plasmid was strongly associated with Hokkaido native horses as has already been observed in virulent isolates from Hokkaido native horses at Bekkai, Hokkaido.