The clustering of isolates from pneumonic cases observed in this study suggests that pathogenic strains of M. arginini may exist and that more consideration should be given to the isolation of M. arginini, alone or concurrently with other bacterial species, during diagnostic investigations of small ruminants. Advances in mycoplasma genomics have demonstrated the role of horizontal gene transfer (HGT) in their evolution, with large segments of the genome exchanged between mycoplasma species that share a common host ( Citti and Blanchard, 2013). Non-pathogenic bacterial species could acquire virulence traits through HGT, thus acquiring pathogenicity (Chen et al., 2014). The discovery of HGT in mycoplasma species thus raises the possibility that some clades could derive from a M. arginini strain that acquired some virulence traits from other pathogenic ruminant mycoplasma species.