Characterization of Rhodococcus equi isolates from submaxillary lymph nodes of wild boars (Sus scrofa), red deer (Cervus elaphus) and roe deer (Capreolus capreolus).

Rhodococcus equi is a soil saprophyte and an opportunistic pathogen causing infections in animals, and rarely in humans. The presence of R. equi in tissues and faeces of some wild animal species was demonstrated previously. In this study we characterized R. equi isolates from submaxillary lymph nodes of free-living wild boars (n=23), red deer (n=2) and roe deer (n=2). This is the first description of R. equi strains isolated from tissues of the Cervidae. All isolates were initially recognized as R. equi based on the phenotypic properties. Their identification was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, detection of the choE gene and by sequence analysis of the 16S rRNA and rpoB genes. The presence of three plasmidic genes (traA, vapA and vapB) associated with R. equi virulence was investigated by PCR. In 16 wild boar isolates the traA and vapB genes were detected and they were located on virulence plasmids type 5, 7 or 11. The isolates from cervids and the remaining wild boar isolates were classified as avirulent based on a genotype traA(-)/vapA(-)B(-). In summary, these results confirm that wild boars can be a source of intermediately virulent R. equi strains, and indicate that red deer and roe deer can be a reservoir of avirulent R. equi strains.