Prevalence of virulence plasmids in soil isolates of Rhodococcus equi from 5 horse-breeding farms in Argentina

Abstract

Prevalence, of virulent Rhodococcus equi in isolates from 5 horse-breeding farms with endemic infection in Argentina was investigated: isolates were tested for the presence of virulence plasmid DNA and virulence-associated 15- to 17-kDa protein antigens (VapA) by colony blotting with the monoclonal antibody 10G5. R. equi was isolated from all of the soil samples obtained from the 5 farms with 2.0 × 103 to 3.7 × 104 colony forming units per gram of soil. Virulent R. equi at various levels (ranging from 4.0 to 24.3 % ) was isolated from the 5 farms and appeared in 11.4% (74 of 650 isolates). Of the 74 virulent R. equi, 8 contained an 85kb type I plasmid and 66 contained an 87-kb type I. These results revealed that environments of the horse-breeding farms with endemic infection in Argentina were contaminated with virulent R. equi harboring a virulence plasmid of 85-kb type I or 87-kb type I, which were found in clinical isolates previously reported from Argentina.