Two new variants of the Rhodococcus equi virulence plasmid, 90 kb type III and type IV, recovered from a foal in Japan

Abstract

This report describes the discovery of two new virulence plasmid types from a crossbred foal with Rhodococcus equi pneumonia in Kumamoto died with severe R. equi pneumonia and ulcerative enteritis. R. equi was isolated in large numbers and isolates from the foal were investigated for the presence of virulence-associated 15–17 kDa antigens (VapA) by colony blotting, using the monoclonal antibody 10G5, and by gene coding for VapA by PCR. Plasmid DNAs extracted from the isolates were digested with restriction endonucleases BamHI, EcoRI, EcoT22I, and HindIII. The digestion patterns that resulted divided the plasmids of these isolates into two closely related types. The digestion patterns were then compared with eight representative virulence plasmid types (85 kb types I, II, III and IV, 87 kb types I and II, 90 kb types I and II), which have already been reported. None of the EcoRI and EcoT22I digestion patterns of the eight representative plasmids matched those of the two plasmid types. We tentatively designated these new plasmid types as 90 kb type III and type IV, since HindIII and BamHI digestion patterns of the two plasmid types were identical with those of a 90 kb type I plasmid. This study, demonstrated that there are at least 10 distinct but closely related plasmids present in isolates from horses in the world.